Conservation of Momentum

5/23/2018 Conservation of Momentum

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CONSERVATION

MOMENCHAPTER 2 FORCE


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The Principle of Conservation of Momentu

The total momentumof in a closed system

constant, if no externalforce acts on the

system.


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Conservation : the total amountof matter /

quantity remainsthe same before and after theoccurrence of an event.

A closed system : the sum of external forcesac

on the system is zero.

Example of an external force is friction.


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The Principle of Conservation of Momentum

shall be discussed in two situations

A collision

The total momentum of

the objects:

before a collision =after the collision

An explosion

The sum of the

momentums remai

zero after an explos


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COLLISCONSERVATION OF


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THERE ARE TWO TYPES OF COLLISIONS.

Elastic Collisions

Two objects collide and move apartafter a

collision.

Inelastic collisions

Formula:

11 + 22 = 11 + 22

Two objects combine and stop, or

together with a common velocity a

collision.

Formula:

11 + 22 = 1 + 2


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There are two types of collisions. The first is an inelastic collisi

which is more common in everyday life.

During an inelastic collision, some of the kinetic energy, or

movement energy, is lost on impact. This energy is converted another type of energy, such as sound or heat.


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An elastic collision occurs when the total kinetic energy, o

movement energy, of two or more objects is the same aft

collision as before the collision.

Unlike an inelastic collision, no energy is transformed into another typeCompletely elastic collisions dont usually happen in the real world, asi

from between subatomic particles, but the collision between two billia

is a close approximation.


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Another example of approximateelastic collisions

When the 1stball is pulled to the side and then released so as fall back and strike t

ball.

It is observed that the 1stball stops, but the last ball swings out to the same heigh

which the ball P was released.

This shows the last ball possesses the same amount of momentumand kinetic e

as 1stball before it struck the 2ndball.

The total momentum of the ball: before a collision = after the collision


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Activity 2.3

To verify the principle of conservation of

momentum in

Elastic collisions, and Inelastic collisions Apparatus / Materials:

Ticker-timer, 12 V a.c. power supply, runway, 4 trolleys, wooden block,

tape, cellophane tape, and plasticine.


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Procedure:

The runway is adjusted to compensate the friction.

Trolley A with a spring-loaded piston is placed at the higher end of the

and trolley B is placed halfway down the runway and stayed at rest.

Two ticker tapes are passed through the ticker timer, one attached to t

and another attached to trolley B.

The ticker-timer is switched on and trolley A is given a slight push so th

moves down the runway at a uniform velocity and collides with trolley

which is stationery.

After collision, the two trolleys move separately.


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RESULT:

Ticker-tape obtained:

Trolley A Trolley B


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DISCUSSION

The spring-loaded piston acts as a spring buffer in the collis

order to make the trolley bounce off the other one.

Strictly speaking, this collision is not a perfect elastic collision

part of the kinetic energy of the colliding trolley changes to sor heat energy during the collision.


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CONCLUSION:

Total momentum before collision = total momentum

collision

The principle of conservation of momentum is verifie


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INELASTIC COLLISION


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PROCEDURE:

The runway is adjusted to compensate the friction.

The spring loaded piston of trolley A is removed and some plasticine is paste

trolley A and B.

A ticker tape is attached to trolley A only.

The ticker-timer is switched on and trolley A is given a slight push so that it m

down the runway at a uniform velocity and collides with trolley B which is sta

After collision, the two trolleys are move together.


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RESULT

Conclusion:

Total momentum before collision = total momentum after c

The principle of conservation of momentum is verified.


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EXERCISE:

1.

Block A of mass 5 kg is moving with velocity 2 m s-1a

collides with another stationery block B of unknown

After the collision, block A moves with velocity 0.5 m

Given that the collision is elastic. Find the momentum

block B after the collision.


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2

A truck travels at a velocity of 15 m s-1collides

head-on with a car that travels at 30 m s-1. The

of the truck and the car are 6000 kg and 1500 k

respectively. What is the final velocity of the tw

vehicles after the collision if they stick together


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3

An astronaut of mass 90kg moves at a velo

of 6ms-1and bumps into a stationary astro

of mass 100kg. How fast do the two astron

move together after collision?


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4

A 50kg skater is moving due east at a speed of 3

before colliding into another skater of mass 60k

moving in the opposite direction at a speed of 71. After the collision, the two skater hold on to

other. In which direction will they move? What

the speed of the two skaters?


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5

A trolley of mass 3 kg moving at a velocity of 2

collides with another trolley of mass 0.5 kg whi

moving at a velocity of 1 ms-1 in the same direc

If the 0.5 kg trolley moves at a velocity of 2.5 m

the same direction after collision, what is the

velocity of the 3 kg trolley?


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6

The diagram shows two trolleys of different masses before aafter a collision. Find the velocity of the 3 kg trolley after the

collision.

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Conservation of Momentum