### Fall 2004 Physics 101 Hour Exam 2(24 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***.

True-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 98. The exam period was 90 minutes. The mean score was 71.9; the median was 74. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

This and the next two questions concern the same situation:

A 2-kg disk and a 4-kg disk slide on a horizontal frictionless surface. The 2-kg disk is initially traveling in the positive x-direction at 7 m/s, the 4-kg disk is initially traveling in the positive y-direction at 5 m/s. The disks collide and stick together as shown in the figure below.

What is the final speed | v | of the two disks after the collision?

(a)   | v | = 4.1 m/s
(b)   | v | = 8.6 m/s
(c)   | v | = 12 m/s

### QUESTION 2*

At what angle θ, do the two disks travel after the collision?

(a)   θ = 37°
(b)   θ = 55°
(c)   θ = 64°

### QUESTION 3*

The total mechanical energy of the two disks was conserved during the collision.

(T)   True
(F)   False

### QUESTION 4*

This and the next questios concern the same situation:

A massless 100-cm stick has a 2-kg ball on one end, and an 8-kg ball on the other as shown below.

Where is the center of mass located for this system?

(a)   50 cm to the right of the 2-kg ball
(b)   70 cm to the right of the 2-kg ball
(c)   80 cm to the right of the 2-kg ball

### QUESTION 5*

What is the moment of inertia for this system if it is rotated about a point 50 cm to the right of the 2-kg ball?

(a)   I = 2.5 kg m2
(b)   I = 5.0 kg m2
(c)   I = 10 kg m2

### QUESTION 6*

This and the next question concern the same situation:

A uniform one-meter bar has a mass of 10 kg. One end of the bar is hinged to a building, and the other end is suspended by a cable that makes an angle of 45° above the horizontal as shown in the picture.

What is the tension T in the cable?

(a)   |T| = 69 N
(b)   |T| = 98 N
(c)   |T| = 113 N
(d)   |T| = 129 N
(e)   |T| = 132 N

### QUESTION 7**

What is the vertical component of the force exerted by the hinge?

(a)   | Fy | = 0
(b)   | Fy | = 26 N
(c)   | Fy | = 49 N
(d)   | Fy | = 72 N
(e)   | Fy | = 98 N

### QUESTION 8*

This and the next three questions concern the same situation:

A three-meter plank has a mass of 15 kg and is supported by two saw-horses as shown below. The first saw-horse is at the right end, and the second saw-horse is two meters to the left of the first.

What is the force that the left saw-horse provides to support the plank?

(a)   F2 = 73.5 N
(b)   F2 = 110 N
(c)   F2 = 147 N

### QUESTION 9*

What is the force that the right saw-horse provides to support the plank?

(a)   F1 = 37 N
(b)   F1 = 73.5 N
(c)   F1 = 147 N

### QUESTION 10**

What is the largest distance d to the left of saw-horse 1 that a 10 kg mass can be placed without tipping the plank?

(a)   d = 2.35 m
(b)   d = 2.5 m
(c)   d = 2.75 m

### QUESTION 11*

When the 10-kg mass is at this position (at the largest distance from saw-horse 1 possible without tipping), what is the force that the left-saw horse provides to support the plank with the mass on it?

(a)   F2 = 73.5 N
(b)   F2 = 123 N
(c)   F2 = 245 N

### QUESTION 12*

This and the next question concern the same situation:

A 4-kg block, starting at rest, is moved a distance d = 3 meters across a horizontal frictionless floor by a force F at an angle θ = 31° with respect to the floor, as shown in the figure. The force does work in the amount of 44 J on the block during the displacement.

What is the magnitude of the force?

(a)   7 N
(b)   15 N
(c)   17 N

### QUESTION 13*

How fast is the block moving after it has traveled the 3 meters?

(a)   v = 1.5 m/s
(b)   v = 2.3 m/s
(c)   v = 3.8 m/s
(d)   v = 4.7 m/s
(e)   v = 5.1 m/s

### QUESTION 14**

This and the next two questions concern the same situation:

A skier starts at rest from the top of a hill at height h above ground. The skier glides down the hill to point A and continues up a second hill 9 meters high and back down the other side. Her entire trip up to point C is frictionless. After point C, there is friction between her skis and the ground. She comes to a complete stop 53 meters after point C, at point D.

Of the three listed below which is the smallest value of the height h so that the skier reaches point C?

(a)   5 m
(b)   10 m
(c)   15 m

### QUESTION 15*

If the height h = 22 m, what is the speed of the skier at point A?

(a)   v = 4 m/s
(b)   v = 13 m/s
(c)   v = 21 m/s
(d)   v = 35 m/s
(e)   v = 44 m/s

### QUESTION 16**

If the height h = 22 m, what is the friction coefficient between the skis and the ground after point C?

(a)   0.1
(b)   0.2
(c)   0.3
(d)   0.4
(e)   0.5

### QUESTION 17**

This and the next two questions concern the same situation:

A 2-kg block is released from rest and slides down an incline with angle θ = 41°. The coefficient of kinetic friction between the block and the incline is 0.27. The block goes down a distance D along the incline where it hits a wall and rebounds. Just before it hits the wall, the block has a speed v = 3 m/s.

What is the distance D traveled by the block on the incline on its way down?

(a)   1 m
(b)   2 m
(c)   3 m
(d)   4 m
(e)   5 m

### QUESTION 18**

What is the work done by gravity on the block as it slides down the ramp?

(a)   3 J
(b)   5 J
(c)   9 J
(d)   11 J
(e)   13 J

### QUESTION 19***

The collision between the block and the wall is elastic and lasts 0.06 seconds. What is the average force on the block during the collision?

(a)   100 N
(b)   200 N
(c)   300 N

### QUESTION 20***

This and the next two questions concern the same situation:

Two 5-kg blocks are connected by a taught, massless string that runs over a massless pulley. The first block is on a horizontal frictionless surface and the right block slides down a frictionless incline. The blocks start from rest with the right block at the top of a frictionless incline that has a height of 0.8 m, as shown.

Calculate the speed of the right-side 5-kg block after the it reaches the bottom of the incline, assuming that the left-side 5-kg block does not hit the pulley.

(a)   v = 2.8 m/s
(b)   v = 4.0 m/s
(c)   v = 4.6 m/s

### QUESTION 21***

Now the experiment is repeated with a new pulley. The massless pulley is replaced by a pulley with a mass of 10 kg, and radius of 0.15 meters (I = 1/2 M R2). Calculate the speed of the right 5-kg block after it reaches the bottom of the incline.

(a)   v = 1.1 m/s
(b)   v = 2.1 m/s
(c)   v = 2.3 m/s
(d)   v = 2.7 m/s
(e)   v = 3.2 m/s

### QUESTION 22**

If the massive pulley in the previous question is now replaced by a pulley with twice the radius and half the mass, the speed of the right block when it reaches the bottom of the incline is

(a)   larger than that in the previous problem.
(b)   equal to that in the previous problem.
(c)   smaller than that in the previous problem.

### QUESTION 23*

This and the next question concern the same situation:

A bullet with an initial velocity of 280 m/s in the +x-direction penetrates an initially stationary block of mass 11 kg and emerges on the other side with a final velocity of 70 m/s in the +x-direction. The velocity of the block after the collision is 0.2 m/s, also in the +x-direction. Assume the block slides on a horizontal frictionless surface.

What is the mass of the bullet?

(a)   0.01 kg
(b)   0.02 kg
(c)   0.03 kg
(d)   0.04 kg
(e)   0.05 kg

### QUESTION 24*

If the bullet were to get stuck in the block during the collision, the final speed of the block would be

(a)   smaller than 0.2 m/s.
(b)   equal to 0.2 m/s.
(c)   larger than 0.2 m/s.

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.