Introductory Quiz

It may seem strange to start a course with a quiz, but it is important for you to take this quiz, especially because this course is for people with "some knowledge of mechanics":

1. It will give us important insight into what you and the class bring to the course in terms of various skills.

2. It will give you practice taking a quiz (and will not count in your grade).

3. It will give you an idea of the variety of problem types you'll experience in this course.

4. In the future analysis of these data we will be able to give new students guidance on whether they're ready for this course.

So we hope you will make a conscientious effort to do well on this quiz.

Sincerely,

Dr. Pritchard

Car Crash Investigation

(0.5 puntos posibles)

You are a policeman investigating a car crash. Car #1 crashed into a stationary car #2. There is no indication that the driver of car #1 applied the brakes before the collision. After the collision, the two cars stuck together and slid until they came to rest.

Part 1

Your goal is to determine whether car #1 was speeding before the collision. Consider the following steps for determining the speed of car #1.

1. Measure the length (d) of the skid marks for the cars to determine how far they slid after the crash.

2. Look up the coefficient of kinetic friction ( μ ) between the car tires and the ground.

3. Look up the masses of the two cars (m 1 , m 2 ).

4. Find the amount of work done by friction as the cars slide, using the definition of work: Work=∫F ⃗ ⋅dx ⃗ =−μ(m1+m2)gd.

5. Use conservation of energy to determine the speed of the cars just after the crash, vf, via the equation 12(m1+m2)v2f=μ(m1+m2)gd.

6. Use conservation of energy to determine the initial velocity of the first car, v1, via the equation 12m1v21=12(m1+m2)v2f.

7. Compare v1 to the speed limit to see whether the car was speeding.

That solution has an error. At what step does this error appear? (Enter a number from 1 to 7).

En el paso 4.

Car Crash Investigation, Part 2

(0.5 puntos posibles)

How do you know that the error is there?

The approach described is valid, but the equation listed in this step is incorrect.

Esto debido a que la expresión: ∫ F⃗×d x⃗≠W

Blocks on Ramp

(1 punto posible)

Acceleration of a Block on a Ramp

The diagram depicts a block sliding along a frictionless ramp. The eight numbered arrows in the diagram represent directions to be referred to when answering the next two questions.

The direction of the acceleration of the block, when in position II, is best represented by which of the arrows in the diagram?

The direction of the acceleration of the block (after leaving the ramp) at position III, is best represented by which of the arrows in the diagram?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

After I study a topic in physics and feel that I understand it, I have difficulty solving problems on the same topic.

Pendulum Swing

(3 puntos posibles)

The pendulum shown below is released from rest at the horizontal position labeled P, passes the midway point M on its descent to the bottom B of its swing.

Which of the 8 arrows shown in the diagram most closely represent the direction of acceleration at each of the following points?

At the starting point P:

At the middle point M:

At the bottom point B:

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

I do not expect physics equations to help my understanding of the ideas; they are just for doing calculations.

Center of mass

(1 punto posible)

Two small particles of mass m1 and mass m2 attract each other with a force that varies with the inverse cube of their separation. At time t0, m1 has velocity v directed towards m2, which is at rest a distance d away. At time t1, the particles collide.

How far does m1travel in the time interval (t0 and t1)

Note: you may use t1 and t0 in your answer. Enter m_1, m_2, t_1 and t_0 for m1, m2, t1 and t0.

DATOS: F= 1

d3; COMO: F=ma ENTONCES:

1

d3×m=a

Por datos del problema m2 parte del reposo y m1 tiene un valor de velocidad inicial y cada una se acerca a la otra

Sea x la distancia que recorre m1 e y la distancia que recorre m2:

x+ y=d

ENTONCES: xf= x0+( v 0×t )+( 12×a× t2)REEMPLAZANDO: xf=v (t 1−t 0)+

( t 1−t 0 )2

2md3

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

I can usually figure out a way to solve physics problems.

Vertical Spring

(1 punto posible)

A light spring with a force constant k is suspended from the ceiling as shown. A block of mass m is attached to it. Initially, the block is held so that the spring is not stretched. The block is then released. The acceleration due to gravity is g.

Part 1. What is the maximum elongation of the spring in the subsequent motion of the block?

Part 2. Eventually, after multiple up-and-down cycles, the block comes to rest. How much heat is generated during the motion of the block?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

It is important for the government to approve new scientific ideas before they can be widely accepted.

Blocks in Elevator

(1 punto posible)

Blocks I and II, each with a mass of 1.0 kg, are hung from the ceiling of an elevator by ropes 1 and 2. What is the force exerted by rope 1 on block I when the elevator is traveling upward at a constant speed of 2.0 m/s?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

If I get stuck on a physics problem, there is no chance I’ll figure it out on my own.

Spring and Mass

(1 punto posible)

Consider an ideal spring that has an unstretched length l and a spring constant k. Suppose the spring is attached to a mass m that lies on a horizontal frictionless surface. The spring-mass system is compressed a distance of x_0 from equilibrium and then released with an initial speed v_0 toward the equilibrium position.

What is the maximum distance the spring will be stretched?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

If I want to apply a method used for solving one physics problem to another problem, the problems must involve very similar situations.

BOY ON A SWING SET

(1 punto posible)

P and R mark the highest and Q the lowest positions of a 50kg boy swinging as illustrated in the following figure.

What is the tension in the rope at point Q?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

If I don’t remember a particular equation needed to solve a problem on an exam, there’s nothing much I can do (legally!) to come up with it.

FORCE IN AN ELEVATOR

(1 punto posible)

A woman weighing 6.0×102N is riding an elevator from the first floor to the sixth floor. As the elevator approches the sixth floor, it decreases its upward speed from 8.0 to 2.0 m/s in 3.0s. What is the average force exerted by the elevator floor on the woman during this 3.0s interval?

PHYSICS LEARNING ATTITUDE SURVEY

On a scale of 1-5, to what extent do you agree with the following statement?

I enjoy solving physics problems.

PUCKS ON ICE

(1 punto posible)

The diagram below depicts two pucks on a frictionless table. Puck B is four times as massive as puck A. Starting from rest, the pucks are pushed across the table by two equal forces.

Which puck has the greater kinetic energy upon reaching the finish line?

SPINNING MASSES ON A ROD

A piece of scientific apparatus can be viewed approximately as two masses connected by strings, and rotating horizontally about an axis with angular speed ω. The apparatus is mounted on a satelite, so gravity is negligible in this case. Given m1, m2 and the length of the rope d, find T1 the tension in the rope connecting m1 to the axis.

Give an equation for T1 in terms of omega (ω), m_1 (m1), m_2 (m2), and d (d).