### Spring 2003 Physics 101 Hour Exam 2(25 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 ***.

This exam consists of 25 questions; 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 111. When the exam was given, the mean was 91.5; the median was 95. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

This and the next three questions concern the same situation:

A 10 kg box initially stands still on a horizontal frictionless surface. A force F = 15 N is applied horizontally to the box, and the box moves 25 m. What is the work done on the box by the force F ?

(a)   0 J
(b)   150 J
(c)   375 J
(d)   425 J
(e)   1250 J

### QUESTION 2*

What is the velocity of the box after it has traveled a distance of 25 m ?

(a)   2.4 m/s
(b)   8.7 m/s
(c)   15.0 m/s
(d)   25 m/s
(e)   27.4 m/s

### QUESTION 3**

Consider the case where there is friction between the box and the horizontal surface. The same force F=15 N is applied horizontally and the box moves the same distance of 25 m. Compared to the work done by the force F on the box when the surface is frictionless, the work done by the force F on the box in the presence of friction is

(a)   smaller.
(b)   the same.
(c)   greater.

### QUESTION 4*

Consider the case where the force F = 15 N is applied at an angle of 30° upward with respect to horizontal. The box moves along the horizontal frictionless surface the same distance of 25 m. Compared to the work done by the force F when it is applied horizontally, the work done by the force F when it is applied at a 30° angle is

(a)   smaller.
(b)   the same.
(c)   greater.

### QUESTION 5*

This and the next two questions concern the same situation:

A basketball of mass 0.5 kg is released from rest at an initial height of 2 m above the floor. It falls, hits the floor, and bounces back up to a maximum height of 1.2 m above the floor.

What is the work Wg done by gravity on the ball as it falls from its initial height down to a point just before it hits the floor?

(a)   Wg = 0 J
(b)   Wg = 1 J
(c)   Wg = 4.9 J
(d)   Wg = 9.8 J
(e)   Wg = 19.6J

### QUESTION 6**

What is the change in kinetic energy of the ball, ΔKE, as it falls from its initial height down to a point just before it hits the floor?

(a)   ΔKE = Wg
(b)   ΔKE = -Wg
(c)   ΔKE = 0

### QUESTION 7*

How much mechanical energy is lost due to the collision with the floor?

(a)   0 J
(b)   1 J
(c)   3.9 J
(d)   7.8 J
(e)   9.8 J

### QUESTION 8*

This and the next question concern the same situation:

A car of mass 1500 kg collides head-on with a truck of mass 9000 kg. After the collision, the wreckage is at rest. The speed of the car just before the collision was 30 m/s. What was the speed of the truck just before the collision?

(a)   5 m/s
(b)   10 m/s
(c)   15 m/s
(d)   30 m/s
(e)   60 m/s

### QUESTION 9*

Compare the magnitude of the impulse exerted on the car by the truck, IC, to the magnitude of the impulse exerted on the truck by the car, IT.

(a)   IC = IT
(b)   IC = 6 IT
(c)   IC = IT / 6

### QUESTION 10*

A bullet having an initial velocity of 300 m/s in the +x direction penetrates an initially stationary pop can of mass 100 gm and emerges on the other side with a final velocity of 200 m/s in the +x direction. The velocity of the pop can after the collision is 5 m/s, also in the +x direction. Assume the pop can slides on a horizontal frictionless surface. What is the mass of the bullet?

(a)   2 gm
(b)   5 gm
(c)   12 gm
(d)   21 gm
(e)   25 gm

### QUESTION 11**

Two blocks, one of mass M and the other of mass 2M, are on a horizontal frictionless surface and are initially at rest. Each block is now acted on by the same constant force F for the same time interval Δt.

After the force acts, which block has the larger momentum?

(a)   The block of mass M.
(b)   The block of mass 2M.
(c)   The two blocks have the same momentum.

### QUESTION 12**

This and the next question concern the same situation:

A ball of mass M is released from rest a height H above a horizontal floor. It hits the floor and bounces back up to its original height H. What is the magnitude of the impulse exerted by the floor on the ball during the collision?

(a)   M sqrt(2gH)
(b)   2M sqrt(2gH)
(c)   0

### QUESTION 13*

Suppose instead that the ball is released from rest from the same height H, but sticks to the floor rather than bouncing. Compared with the previous problem, the magnitude of the impulse exerted by the floor on the ball will now be

(a)   the same.
(b)   greater.
(c)   less.

### QUESTION 14*

Two blocks slide towards each other on a horizontal frictionless surface. Block 1 has a mass of 10 kg and initially slides to the right with speed 10 m/s. Block 2 has a mass of 6 kg and initially slides to the left with speed 15 m/s. After they collide, block 2 slides to the right with speed 10 m/s, and block 1 slides to the left (see picture).

What is the speed of block 1 after the collision?

(a)   v1,f  = 0 m/s
(b)   v1,f  = 5 m/s
(c)   v1,f  = 10 m/s
(d)   v1,f  = 15 m/s
(e)   v1,f  = 20 m/s

### QUESTION 15**

A bomb is initially at rest when it suddenly explodes into three pieces. A 5-kg piece goes north at 6 m/s, and a 2-kg piece goes east at 20 m/s. What is the magnitude of the momentum of the third piece? (You can ignore any effects due to gravity).

(a)   30 kg-m/s
(b)   35 kg-m/s
(c)   40 kg-m/s
(d)   45 kg-m/s
(e)   50 kg-m/s

### QUESTION 16**

This and the next question concern the same situation:

A 60 kg skier slides down a gentle slope with a constant velocity. The length of the slope is 1 km, and the vertical drop is 200m (see picture).

In going from the top of the hill to the bottom, the total work done on the skier by all forces is

(a)   positive.
(b)   negative.
(c)   zero.

### QUESTION 17**

Calculate the work done by the frictional force on the skier as he goes from the top of the hill to the bottom.

(a)   Wf = 0
(b)   Wf = 1.2 × 105 J
(c)   Wf = 5.9 × 105 J
(d)   Wf = -1.2 × 105 J
(e)   Wf = -5.9 × 105 J

### QUESTION 18*

This and the next two questions concern the same situation:

A car drives on a straight horizontal road and its wheels roll on the ground without slipping. The radius of the front wheels is Rfront = 0.30 m and the radius of the rear wheels is Rrear = 0.35 m. The front wheels rotate with an initial angular velocity of ωF0 = 88 rad/s.

What is the initial speed of the car?

(a)   18.3 m/s
(b)   26.4 m/s
(c)   32.8 m/s
(d)   61.7 m/s
(e)   88.0 m/s

### QUESTION 19*

During the time that a rear wheel makes exactly one complete revolution, a front wheel

(a)   makes more than one revolution.
(b)   makes less than one revolution.
(c)   also makes exactly one revolution.

### QUESTION 20*

At t = 0 the driver of the car applies the brakes. The car slows with uniform acceleration, and comes to rest at t = 4 s.

What is the angular velocity of a front wheel at t = 1 s ?

(a)   33 rad/s
(b)   44 rad/s
(c)   55 rad/s
(d)   66 rad/s
(e)   77 rad/s

### QUESTION 21*

This and the next two questions concern the same situation:

A uniform plank and a bowling ball have the same mass M. The length of the plank is 5m and it rests horizontally on two supports, as shown in the drawing, with 2m of the plank hanging over the right support.

To what distance xtip (measured from the right-most support) can the bowling ball be rolled onto the overhanging part of the plank before the plank just begins to tip?

(a)   xtip = 0.3 m
(b)   xtip = 0.5 m
(c)   xtip = 0.7 m
(d)   xtip = 0.8 m
(e)   xtip = 0.9 m

### QUESTION 22**

When the ball is located at xtip, what is the magnitude of the upward force exerted on the plank by the left post?

(a)   0
(b)   Mg
(c)   2Mg

### QUESTION 23**

When the ball is located at xtip, what is the magnitude of the upward force exerted on the plank by the right post?

(a)   0
(b)   Mg
(c)   2Mg

### QUESTION 24*

This and the next question concern the same situation:

One end of a massless horizontal beam is attached to a vertical wall by a hinge, and the other end is supported by a string which is also attached to the wall. In case 1, as shown in the figure, a ball of mass M is hung from the end of the beam, while in case 2, an identical ball is hung from the middle of the beam.

How does the tension in the string attached to the wall compare between the two cases?

(a)   T1 > T2
(b)   T1 < T2
(c)   T1 = T2

### QUESTION 25***

What is the tension in the string attached to the wall in case 2?

(a)   T2 = Mg / 2
(b)   T2 = Mg
(c)   T2 = 2 Mg

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.