thequarkyteacher.files.wordpress.com€¦ · Web viewmomentum, the cannon must move backwards when the ball moves forwards. Equilibrium. A system where both the vertical forces

Edexcel ScienceiGCSE Physics

P. Moments and Momentum

Name:________________Physics Teacher:______________

House CG Test Score

Year 11

Specification Checklist

1.01 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and newton/kilogram (N/kg)

1.02 use the following units: newton metre (Nm), kilogram metre/second (kg m/s)

1.11 describe the effects of forces between bodies such as changes in speed, shape or direction

1.13 understand how vector quantities differ from scalar quantities

1.14 understand that force is a vector quantity

1.25 know and use the relationship between momentum, mass and velocity:

momentum = mass × velocity

p = m × v

1.26 use the idea of momentum to explain safety features

1.27 use the conservation of momentum to calculate the mass, velocity or momentum of objects

1.28 use the relationship between force, change in momentum and time taken:

Force=Change∈Momentumtime taken

1.29 demonstrate an understanding of Newton’s third law

1.30 know and use the relationship between the moment of a force and its perpendicular distance from the pivot:

moment = force x perpendicular distance

1.31 know that the weight of a body acts through its centre of gravity

1.32 use the principle of moments for a simple system of parallel forces acting in one plane

1.33 understand for the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam

Moments and Momentum – Science (Physics) 2

Force

Force

Force

Key Definitions

Key Word Image Definition

Conserve Keep the same.

In the example, the motion at the start is zero. To conserve momentum, the cannon must move backwards when the ball moves forwards.

Equilibrium A system where both the vertical forces and the turning forces are balanced.

Fulcrum Another term for a pivot

Lever A straight arm that rotates around a pivot. E.g. the handle of a hammer.

Light beam A ‘plank’ or structure with negligible mass that is supported at both ends

Moment A turning force or a rotational effect. The product of a force and the perpendicular distance from the pivot.

Momentum The product of an object’s velocity and mass. The more massive the object. The more momentum at the same speed.

The greater the speed of an object, the greater the momentum.

Perpendicular At an angle of 90o to a surface.

Pivot The point around which a lever rotates. E.g. a door hinge.

Vector Something with both Magnitude and Direction


Velocity

Velocity

Small Momentum

Larger Momentum

1: Moments Recap

Knowledge and Understanding Quiz Use the knowledge you have gained so far in the topic to answer the following questions

1. The front crumple zone of a car is tested at a road traffic laboratory. This is done by using a remote control device to drive the car into a strong barrier. Electronic sensors are attached to a dummy inside the car.

(i) Draw an arrow in Box 1 to show the direction of the force that the car exerts on the barrier.

(1)(ii) Draw an arrow in Box 2 to show the direction of the force that the barrier exerts on the car.

(1)

(iii) The car exerts a force of 5000 N on the barrier. The barrier does not move.

(1)

2. The stopping distance or a car has two parts. Complete the diagram below by adding an appropriate label to the second part of the stopping distance.

_______________________________ (1)

(ii) State one factor that changes both the first part and the second part of the stopping distance.

(1)

Total: /5


more than

The force exerted by the barrier on the car will be equal to 5000 N.

less than

Learning Outcomes:

1. Know and use the equation to calculate the moment of a force:moment=force× perpendicular distance ¿ the pivot

2. Use the principle of moments to solve problems.3. Describe how the upward forces on a light beam vary when I put a heavy object at

different positions on the beam.

Moments Summary

A moment is the turning effect of a force

MOMENT (Nm) = FORCE (N) x perpendicular DISTANCE from the pivot (m)

The principle of moments states that when the clockwise moments are equal to the anticlockwise moments a body will be in

equilibrium.


A force can make an object turn around a pivot point.

We can increase the turning effect by:

Increasing the force Increasing the distance from

the pivot

Objects can turn clockwise or anticlockwise – it depends which moment is larger. There will be a resultant moment.

If the anticlockwise moment is equal to the clockwise moment then an object is balanced (or in equilibrium).

When an object is stationary the forces on it must be balanced.

For a bridge or plank supported at two ends – the upward force must equal the downward force.

BUT as the object on the bridge is moved across, the size of the forces at the supports will change.

The force will always be larger at the end closer to the object.

Worked Examples

1. Find the missing force for the plank

2.

a) Find the moment of the girl about the point A.

b) The diving board is in equilibrium.

(i) Draw the force exerted on the diving board by the support

(ii) What is the moment given by the support about point A?

(iii) If the support is 1.5m away from point A, what is the force exerted by the support on the diving board?


Worksheet: Moments Calculations

1. Calculate the moment on the following seesaws

2. Are the following balanced or unbalanced?

a) John is 0.5m from the pivot, Peter is 1m from the pivot?

b) John is 1m from the pivot, Peter is 1.4m from the pivot?

c) John is 0.4m from the pivot, Peter is 0.56m from the pivot?

d) John is 1.2m from the pivot, Peter is 1m from the pivot?

3. What is the missing force?

4. Child A has a weight of 250N. If the seesaw is balanced, how far away must she be sat from the pivot?


5kg 4m 10kg 1.5m

5.

a) Show that the crane is unbalanced.

b) What does the mass of the counterweight need to be to balance the 600kg load?

6. What is the value of d if the plank is balanced?

7. Explain how the forces acting on the supports of the bridge change as the car drives across the bridge.

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8. The diagram shows a clock on a trolley. The trolley is being used to move the clock.

Explain how making the trolley taller affects the moment produced by the 64 N force about the pivot?

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9. The diagram shows a father and his two children sitting on a playground see-saw. The see-saw is not moving.

What is the weight of the boy?

Explain what will happen, using ideas involving moments, when the father gets off the see-saw

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1: Momentum

Knowledge and Understanding QuizUse the knowledge you have gained since Shell to answer the following questions:

1. In what direction does friction act?

……………………………………………………………… (1)

2. What is the resultant force on an object that has 25N pulling it right and 12N pulling it left?

………………………………………………………………………………………… (2)

3. Label all the forces on the diagram below:

(4)

4. What is the definition of a transverse wave?

…………………………………………………………………………………………

………………………………………………………………………………………… (2)

5. What is the equation linking force, pressure and area?

(1)

6. Sketch a graph to show the difference between ac and dc.

(2)

7. What are the units of charge?

……………………………………………………………… (1)

Score [ /13]


Learning Outcomes:

1. Describe what factors affect the momentum of an object2. Use and rearrange the equation:

momentum = mass x velocityp=m×v

Momentum

Key Ideas

1. Momentum is a vector quantity (has magnitude and direction)2. Momentum is measured in kg m/s (kilogram meters per second)

3. Momentum, mass and velocity(speed) are linked by the equation:Momentum=mass×velocity p=m×v

4. To use this equations mass must be measured in kilograms and velocity in m/s.5. An object can increase its momentum by:

a. Increasing its massb. Increasing its velocity

Worked Examples

1. What is the momentum of a 500kg car travelling at 15m/s?

2. If a train has a momentum of 20000kg m/s a mass of 900kg, how fast is it travelling?

Worksheet – Momentum


Complete the questions below using the equation you have just learnt. You must show all your working [equation, substitution, solution and units]

1. If a ball of mass 1.5 kg travels at a velocity of 1.6 m/s, what is the momentum?

…………………..

2. Calculate the momentum of a boy with mass 55 kg if he travels at a velocity of 6 m/s.

…………………..

3. What is the momentum of a car with a mass of 1000 kg traveling at 60 m/s?

…………………..

4. Calculate the velocity of a dog with a mass of 12 kg and with a momentum of 20 kg m/s.

…………………..

5. Calculate the velocity of a boy with a mass of 35 kg and has a momentum of 60 kg m/s.

…………………..

6. What is the mass of a car if the velocity is 60 m/s and the momentum 3000 kg m/s?

…………………..

7. A lorry hits a car. The lorry has a mass of 2500 kg and travels at 30 m/s. The car has a mass of 1000 kg and is travelling at 35m/s. How much larger is the momentum of the lorry than the car?


…………………..

8. What is the momentum of a plate with a mass of 650g if it is falling at a speed of 10m/s?

…………………..

9. Calculate the velocity of a toy car with a mass of 15g and with a momentum of 0.0075 kg m/s.

…………………..

10. Who is travelling faster: a kitten has a mass of 950g with momentum 0.43kg m/s or a bird with mass 475g and momentum 0.38kg m/s?

…………………..

11. A cyclist covers 250m in 30s. If the cyclist and the bike have a combined mass of 85kg, what is the momentum of the cyclist?

…………………..


P1: Investigating Momentum

In this investigation you are going to:

use light gates to find the speed of an object find out how changing the mass changes the speed calculate momentum compare the momentum before and after

Take notes in the box below on how to set up the data-logger to measure the speed at A and then at B

Method

1. Set up the apparatus as shown in the diagram below2. Measure the mass of the trolley with the interrupt card.3. Programme the light gates (as shown by your teacher) to measure the velocity of the

trolley at light gate 1 and light gate 24. Push the trolley and once past light gate 1 ADD some extra mass to the trolley5. Record the velocity at light gate 1 and light gate 2 in your table6. Measure the final mass of the trolley (with the extra mass on it)7. Repeat steps 2-6 with a range of different speeds

8. Optional extra – change the mass you add onto the trolley too


Health and Safety Check!

I will ensure the trolley isstopped safely

I will take care not to drop masses

Results

Mass at start(kg)

Velocity at gate 1(m/s)

Momentum at gate 1(kgm/s)

Mass at end(kg)


Momentum at gate 2(kgm/s)

Analysis

What patterns do you see in your results?

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Further Analysis

Monica did the same experiment as you and her data is found below. However, Chandler rubbed out some of her data.

Mass at start(kg)


Momentum at gate 1(kg m/s)

Mass at start(kg)


Momentum at gate 2(kg m/s)

0.20 0.80 0.16 0.25 0.64

0.30 0.90 0.27 0.54 0.27

0.70 0.28 0.80 0.35

0.50 1.10 0.75 0.55 1.00

1. Fill in the missing values.

2. Correct the mistake Monica has made in her results

3. What happens to the velocity when more mass is added?

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4. What do you notice about the momentum before and after the mass was added?

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5.


Think back to the work you have done on forces and acceleration…

WHY do you think the velocity changes when more mass is added?

4. Conservation of Momentum

Knowledge and Understanding QuizUse the knowledge you have gained since Shell to answer the following questions:

1. List three factors that affect thinking distance?

……………………………………………………………… (3)

2. Which two parts of the EM Spectrum can be used for cooking?

………………………………………………………………………………………… (2)

3. A submarine descends to 120m below the surface of the water. What is the pressure

difference experienced by the submarine? [The density of water is 1000kg/m3]

(3)

4. What is definition of half life?

…………………………………………………………………………………………

………………………………………………………………………………………… (1)

5. What is the equation linking momentum, mass and velocity?

(1)

6. A lightbulb is 65% efficient. If it is supplied with 650J of electrical energy, how much of

this energy is converted into light energy?

(3)

7. What are the units of momentum?

……………………………………………………………… (1)

Score [ /14]


Learning Outcomes:

1. Explain what is meant by the phrase “momentum is conserved”.2. Use the conservation of momentum to calculate the mass, velocity or

momentum of an object.3. Define what is meant by an explosion and use this to calculate mass or

velocity of an object.

Conservation of momentum

Key Ideas

1. Momentum is conserved in a collision as long as no external forces act.2. The total momentum before the collision is equal to the total momentum after the

collision. 3. When tackling a conservation of momentum problem it is good to split the problem into

“before” and “after”. 4. An explosion is a special case of conservation of momentum where the total

momentum is zero.


Remember momentum is a vector!

P2: Demo – Conservation of Momentum

Your teacher is going to demonstrate the conservationof momentum using the air track.

Questions

1. What is the purpose of an air track [What does it reduce and how?]

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2. How did your teacher measure the velocity of the trolleys?

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3. Why are the weighing scales (balance) used?

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4. How do we know if momentum is conserved?

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Health and Safety Check!

I will ensure the trolley isstopped safely

Worked Examples

1. Two trolleys are on an air track travelling towards each other as per the diagram below:

The mass of trolley A is 2kg and the mass of trolley B is 0.75kg. Following the collision the trolleys stick together. What is the final velocity of the trolleys?

2. Angry bird Red, travelling at 15 m/s collides with a stationary Pig. The mass of Red is 50kg and the mass of Pig is 20kg. Following the collision, Red is travelling at 2m/s. What is the velocity of Pig after the collision?

3. A 57kg male ice skater is facing a 43kg female ice skater. They are at rest on the ice. They push off each other and move in opposite directions. The female skater moves backwards with a speed of 2.5m/s. Determine the velocity of the male skater.


BA

4m/s 5m/s

Worksheet – Conservation of Momentum

Complete the questions below using the equation you have just learnt. You must show all of your working [equation, substitution, solution and units] [Hint: Sketch a diagram!]

1. A car of mass 1000kg travelling at a velocity of 20 m/s collides with a stationary car of mass 1000kg. The vehicles move together after the impact. Calculate their velocity.

…………………..

2. Trolley A, travelling at 20 m/s, collides with a stationary Trolley B. The mass of Trolley A is 5kg and the mass of Trolley B is 2kg. Following the collision Trolley A is travelling at 16m/s. What is the velocity of Trolley B after the collision?

…………………..

3. Car of mass 2000kg travelling at a velocity of 5 m/s collides with a stationary motorbike of mass 500kg. The vehicles move together after the impact. Calculate their velocity.

…………………..

4. A cannon of mass 300kg, with a cannonball of 5kg is fired. The ball moves with a velocity of 50 m/s, calculate the recoil velocity of the cannon.

…………………..


5. A van of mass 5,000kg travelling at a velocity of 10 m/s collides with a stationary car. The vehicles move together after the impact at a velocity of 6 m/s. Calculate the mass of the car.

…………………..

6. A boy of mass 50kg on ice skates throws a ball of 1kg in front of him at a velocity of 2.5 m/s. In which direction will he move and at what velocity?

…………………..

7. A lorry of mass 12,000kg travelling at a velocity of 15 m/s crashes into the back of a moving car of mass 1500kg, travelling at a velocity of 5 m/s. The vehicles move together after the impact. Calculate their velocity.

…………………..

8. A cannon fires a cannon ball of mass 10kg at a velocity of 100 m/s and recoils at a velocity of 2 m/s. What is the mass of the cannon?

…………………..


5. Forces and Momentum

Knowledge and Understanding Quiz – Conservation of MomentumUse the knowledge you gained in the last lesson to answer the questions below:

1. A lorry of mass 12,000kg travelling at a velocity of 2 m/s collides with a stationary car of mass 1500kg. The vehicles move together after the impact. Calculate their velocity.

………………….. (5)

2. A pistol of 0.5kg fires a bullet of 0.05kg at a velocity of 300 m/s, calculate the recoil velocity of the gun.

………………….. (5)

Score [ /10]

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Learning Outcomes:

1. Identify that force and momentum are vector quantities meaning they have both magnitude and direction.

2. Use and rearrange the equation:

force= change∈momentumtime taken

3. Explain safety features in a car using ideas related to momentum and how they limit the force experienced by a passenger.

Force and Momentum

Key Ideas

1. Momentum and Force are vector quantities (have magnitude and direction)2. Force, change in momentum and time taken are linked by the equation:

force= change∈momentumtime taken

= final momenum−initialmomentumtime taken

F=∆ pt

=mv−mut

where u=initial speed , v=final speed3. This can be derived from the equation F=m×a

Worked Examples

1. A 5kg car slows from 10m/s to stationary in 4 seconds. How much force did the car experience?

2. A force of 15N is applied to a box for 26s. What change in momentum would we expect the box to experience in that time?


Worksheet – Force and Momentum

Complete the questions below using the equation you have just learnt. You must show all of your working [equation, substitution, solution and units]

Use the equation below to answer the following questions:

F=∆ pt

1. A man has a mass of 110 kg and he runs at 50 m/s. The man stops in 20 s. What force is required to stop the man?

…………………..

2. Consider a football of mass 2kg, which is stationary on the ground. A man kicks it and his foot is in contact with the football for 0.2 seconds. When the football leaves his foot it is travelling at 5 m/s. How much force was required?

…………………..

3. A car travels at 300 m/s and has a mass of 600 kg. The car comes to a halt at traffic lights. What force is required to stop the car if the time taken is 4 s

…………………..

4. A cat has a mass of 7 kg and runs at 10 m/s. The cat stops in 0.6 s. What force is required to stop the cat?

…………………..


5.a. A car is driving at 30m/s. The passenger has a mass of 70kg. What is the

passenger’s momentum?

…………………..

b. The car drives into the back of a drunk driver who has suddenly stopped for a chicken and stops completely in 1s. How much force did the driver have impacted him upon him?

…………………..6.

a. A driver in a K reg Ford Fiesta has a mass of 72kg. It is travelling at a speed of 25m/s. What is the momentum of the passenger?

…………………..

b. The K reg Ford Fiesta hit a wall and has no air bag, so the driver’s momentum is reduced in just 0.4s. What force would have been impacted on the driver?

…………………..

c. The driver behind the Ford Fiesta is a 15 plate BMW. The passenger has a mass of 68kg and is travelling at 21 m/s. What is the momentum of the passenger?

…………………..

d. The BMW goes into the back of the Ford Fiesta. The BMW does have airbags and so it takes 1.2s for his momentum to change to 0kgm/s. What force would the driver feel on his body?

…………………..



Notes: Car Safety

During a collision, the most effective way to reduce the force experienced by the passengers is to increase the ______________ of the collision.

When there is a car crash, the car, its contents and the passengers decelerate rapidly. They experience large forces because of the change in momentum, which can cause injury.

Modern cars also have safety features that absorb kinetic energy in collisions and increase the time that it takes the passengers to decelerate.

These typically include:

Seat belts – that stretch a little as the body moves forward and stops

Air bags – that cushion the head bringing it to a stop slowly

Crumple zones – that crush in a controlled way over a longer time

These features reduce injuries to the people in the car by absorbing energy when they change shape. They increase the time taken for the change in momentum on the occupants' bodies, reducing the forces involved and injuries.

Exam Q: Worked example:

A magazine article states that: “Wearing a seat belt can save your life in a car crash.”

Use your understanding of momentum to explain how this is correct. (4)

When a car crashes the momentum of the people inside changes to zero.

If they wear a seatbelt, the TIME it takes for them to stop is LONGER

And so the change of momentum happens over a longer time

Which REDUCES the force acting on them so they are less likely to be injured.

Q. Explain, using ideas of momentum, why an airbag will protect a passenger from serious injury during a car crash?

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Key Exam Q: Apply knowledge to a different context

The diagram shows a child on a playground swing. The playground has a rubber safety surface.

(a) The child, with a mass of 35 kg, falls off the swing and hits the ground at a speed of 6 m/s.

(i) Calculate the momentum of the child as it hits the ground

(3)

(ii) After hitting the ground, the child slows down and stops in 0.25 s. Calculate the force exerted by the ground on the child.

Force = ............................................................ N(2)

(b) The diagram shows the type of rubber tile used to cover the playground surface.

Explain how the rubber tiles reduce the risk of children being seriously injured when they fall off the playground equipment.

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.................................................................................................................................(3)

STRETCH: Can you come up with any other safety features that use a similar reasoning?

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6. Newton’s Third Law

Knowledge and Understanding Quiz – Conservation of MomentumUse the knowledge you have gained so far in the topic to answer the following questions

1. A bird of mass 800g is flying at a velocity of 16m/s. What is the momentum of the bird?

………………….. (3)

2. A van of mass 2000kg travelling at a velocity of 15 m/s collides with a stationary car of mass 750kg. The vehicles move together after the impact. Calculate their velocity.

………………….. (5)

7. A person has a mass of 90 kg and he runs at 10 m/s. The person stops in 10 s. What force is required to stop the person?

………………….. (4)

Score [ /12]


Learning Outcomes:

1. State Newton’s Third Law2. Describe examples of Newton’s Third Law in everyday life. 3. Label the reaction force on a diagram.

Newton’s Third Law

Key Ideas

1. Newton’s Third Law state that:‘For every action there is an equal and opposite reaction force’

2. A good example of this is when you sit on a chair. You push down on the chair and the chair pushes back on you.

3. Newton’s 3rd Law forces are always act in pairs. They are the same type of force and the same magnitude, but act in opposite directions and on different objects.


Worksheet – Newton’s Third Law1. For each of the examples below complete the following tasks:

Draw the reaction force arrow State the reaction to the given action. For (h) make up your own example!

2. In the diagram below, can you find six examples of action-reaction pairs?


Stretch Worksheet – How many cats are in the white box? Start by finding the comparative weights of the cat, the bomb and the bucket.

The whole picture is in balance. Remember the principle of moments. (Ignore the weight of the beams, string and the box).

How many boots are in the purple box?


Stretch Worksheet – Newton’s Cradle

Newton’s Cradle is an awesome piece of equipment! It demonstrates a number of different Physics concepts.

Using the knowledge you have gained since the start of Shell, what Physics concepts and ideas can you show in Newton’s Cradle. [If you are stuck – do some research!]

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Stretch Worksheet – Science ‘laws’

People often confuse scientific language that has a different meaning in regular conversations. An excellent example of this is ‘Theory’:

General definition: used in describing what is supposed to happen or be possible, usually with the implication that it does not in fact happen.

Scientific definition: an explanation of an aspect of the natural world that can be repeatedly tested and verified in accordance with the scientific method

Another example of this is ‘law’. Using your computer, can you research the general and scientific definitions of a ‘law’ and then go on to identify the similarities and difference between the two.

General Definition:……………………………………………………………………………………………………………

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Scientific Definition:……………………………………………………………………………………………………………

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Similarities Differences


Momentum and Moments

Past Paper Questions


Q1. Scientists test the safety features of a car by crashing it into a large block of concrete.

A dummy is placed in the driver's seat and the scientists video the crash.

(a) In one test, the dummy and the car travel at 8 m/s. The mass of the dummy is 72 kg.

Calculate the momentum of the dummy.

(2)

Momentum = ........................................................... kg m/s

(b) In another test, the momentum of the dummy changes by 920 kg m/s in a timeof 0.17 s.

Calculate the average horizontal force acting on the dummy during this time.

(2)

Average force = ........................................................... N

(c) These tests help to make our roads safer.

(i) State two factors that affect the stopping distance of a car driven on a road.

(2)

1 ................................................................................................................................................

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2 ................................................................................................................................................

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(ii) Use ideas about momentum to explain how the crumple zone of a car helps to

reduce injuries during a crash.

(3)

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(Total for question = 9 marks)

Q2. A student is playing a game with some empty tins.

(a) He throws a wet cloth of mass 0.15 kg at the tins. The wet cloth moves at a velocity of 6.0 m/s.

(i) State the equation linking momentum, mass and velocity.

(1)

(ii) Calculate the momentum of the wet cloth and give the unit.

(3)

Momentum = ................................ unit. ...................................


(iii) The wet cloth sticks to tin 1.

The mass of tin 1 is 0.050 kg. The cloth and tin 1 move away together.

Calculate their velocity.

(2)

Velocity = ........................................................... m/s

(b) The student throws a bigger wet cloth at the remaining tins.

This wet cloth sticks to tins 2 and 3 and they move away together.

The student concludes

Do you

Explain why.

(2)

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Q3. A lorry carries a load of hot asphalt a runny mixture of small stones and tar.

(a) The mass of the lorry and its load is 17 000 kg. The velocity is 13 m/s.

Calculate the total momentum of the lorry and its load.

(2)

momentum = ........................................................... kg m/s

(b) The lorry stops suddenly and the load slides to the front, as shown below.

Force A and force B are upward forces from the road on the lorry.

(i) Use ideas about momentum to explain why the load slides to the front whenthe lorry stops suddenly.

(2)

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(ii) Use ideas about moments to explain why force B increases when the loadslides to the front.

(3)

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(c) The force on the road from one of the tyres is 53 000 N.The pressure of the air in this tyre is

390 kPa.

(i) State the equation linking pressure, force and area.

(1)

(ii) Calculate the area of this tyre in contact with the road.

(2)

Area = ........................................................... m2



Q4. Newton's Cradle consists of a set of identical solid metal balls hanging by threadsfrom a frame so that they are in contact with each other.

(a) A student initially pulls ball A to the side as shown. The student releases ball A and it collides with ball B.

Each ball has a mass of 100 g.

At the time of collision, ball A has a velocity of 3m/s.

Calculate the momentum of ball A at the time of impact and give the unit.

(3)

momentum ........................................................... unit ...........................................................

(iii) After the collision, ball A stops. Ball E moves away. The other balls remain still.


The momentum of ball E as it moves away is the same as the momentum ofball A at the time of impact.

Give the reason for this.

(1)

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(b) The student then releases balls A and B together as shown below.

Predict what will happen to the other balls after the collision and give a reason foryour answer.

(2)

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Moments Questions

Q1. A student investigates the vertical forces acting on the ends of a horizontal rulerwhen it supports a load.

The ruler hangs from two newtonmeters with a weight suspended from it as shown.

(a) The student moves the weight along the ruler and records forces B and C bytaking readings from the newtonmeters.

(i) Which of these is the independent variable in this investigation?(1)

A Distance A

B Force B

C Force C

D Force D

(ii) Which of these is a controlled variable in this investigation?(1)

A Distance A

B Force B

C Force C

D Force D


(b) The student records these readings.

She plots this graph to show how force C changes with distance A.


(i) Complete the student's graph by labelling the vertical axis.

(1)(ii) Using the same grid and axes, plot a second line to show how force B varieswith distance A.

(3)(iii) Use the lines on the graph to find distance A for which force B and force C areequal.

(1)

Distance = ...................................... cm

(c) Suggest why neither force B nor force C are ever zero during the investigation.(1)

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Q2. The diagram shows the side view of a laptop computer.

A student opens the computer with an upward force of 4.2 N.

The force is applied 0.25 m from the pivot.

(a) Calculate the moment of the force that opens the computer.(2)

Moment = ........................................................... N m

(b) The student finds that 4.2 N is the minimum upward force needed to open thecomputer.

Then the student applies a downward force, F, to close the computer.

Explain why the minimum force needed to close the computer is likely to be lessthan 4.2 N.

(2) ..............................................................................................................................................

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Q3. Photograph C shows a student using an old camera that uses film.

(a) The film is pulled through the camera using lever A. The student pushes on lever A with a force of 7.0 N. The force is applied 0.04 m from the pivot.

Calculate the moment of the force that turns lever A and give the unit.(3)

Moment = ........................................................... unit ...........................................................

(b) When all the film has been used, it is pulled back through the camera using lever R.

The force acting on lever R is only 0.02 m from its pivot.Explain why the minimum force needed to turn lever R is likely to be more than 7 N.

(2) .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. .............................................................................................................................................. ..............................................................................................................................................



Q4. A toy train is placed on the middle of a bridge on a model railway.

The weight of the train acts through its centre of gravity. Ignore the weight of the bridge.

(a) Which row of the table shows the correct values for forces X and Y?

(1)

(b) Describe how force X changes if the train moves from P to Q.

(2).............................................................................................................................................

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Q5. The diagram shows the apparatus used to investigate moments.

The 2 N weight is placed 60 cm from the pivot.

The newtonmeter is placed 10 cm from the pivot.

(a) Calculate the reading on the newtonmeter. Ignore the weight of the ruler.

(3)

reading = ............................................... N

(b) The metre rule is replaced by an iron bar.

The iron bar is 1 m long and has a weight of 10 N.The newtonmeter and the 2 N weight stay in their original position.Explain how this change affects the reading on the newtonmeter.

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MomentumAnd Moments

Spec Point Notes


Momentum and Moments Specification Notes

1.01 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and newton/kilogram (N/kg)

1.04 use the following units: newton metre (Nm), kilogram metre/second (kg m/s)

1.11 describe the effects of forces between bodies such as changes in speed, shape or direction

1.13 understand how vector quantities differ from scalar quantities

Scalars are quantities that only have magnitude (size) Vectors are quantities that have magnitude (size) and direction


1.14 understand that force is a vector quantity

1.25 know and use the relationship between momentum, mass and velocity:

momentum = mass × velocity

p = m × v

1.26 use the idea of momentum to explain safety features

1.27 use the conservation of momentum to calculate the mass, velocity or momentum of objects


1.28 use the relationship between force, change in momentum and time taken:

Force=Change∈Momentumtime taken


1.29 demonstrate an understanding of Newton’s third law

1.30 know and use the relationship between the moment of a force and its perpendicular distance from the pivot:

Moment (Nm) = force (N) x perpendicular distance (m)


1.31 know that the weight of a body acts through its centre of gravity

Centre of Gravity = the point where all the weight seems to be concentrated.

For regular shapes it is the geometrical centre of the object - for example, the centre of a cube or a sphere.

For irregular shapes, hang the object from a point on its edge and the Centre of Gravity will end up vertically below the point you are hanging it from.

Repeat this for two or more points, each time drawing a line vertically down through the point you are hanging it from (and therefore through the Centre of Gravity).

1.32 use the principle of moments for a simple system of parallel forces acting in one plane

If an object is balanced, then the sum of all the anticlockwise moments must equal the sum of all

the clockwise moments.


Clockwise moment = 40 x 1.8 =72NmSo anticlockwise moment must equal 72Nm and the

distance is 1.8mSo force = moment/distance = 72/0.8 = 90N

1.33 understand for the upward forces on a light beam, supported at its ends, vary with the position of a heavy object placed on the beam

The total upward force must equal the downward force, so…A + B = 600N

As the object moves along the plank, the force closer to the object will be larger.When the object is in the middle both forces would be equal.


What must the force be to balance the

seesaw?


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thequarkyteacher.files.wordpress.com€¦ · Web viewmomentum, the cannon must move backwards when the ball moves forwards. Equilibrium. A system where both the vertical forces