### Spring 2002 Physics 101 Hour Exam 2(26 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 26 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 122. When the exam was given, the mean was 102.5; the median was 107. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

This and the next three questions pertain to the following situation:

A block sits at rest on a horizontal surface. It suddenly explodes into two pieces. A piece of mass 4 kg goes to the left and a piece of mass 10 kg goes to the right. Each block slides along the frictionless surface, then up a frictionless ramp. The speed of the 4 kg block is 10 m/s immediately after the explosion.

What is the speed of the 10 kg block immediately after the explosion?

(a)   0 m/s
(b)   2 m/s
(c)   4 m/s
(d)   6 m/s
(e)   8 m/s

### QUESTION 2*

What is the maximum height reached by the 4 kg block on the left slope?

(a)   0.9 m
(b)   3.4 m
(c)   4.5 m
(d)   5.1 m
(e)   7.3 m

### QUESTION 3*

Let h4 be the answer to the previous question. The maximum height reached by the 10 kg block on the right slope is

(a)   equal to h4.
(b)   less than h4.
(c)   larger than h4.

### QUESTION 4*

Eventually the two blocks slide back and collide again and stick together. In what direction do the two blocks move immediately after the collision?

(a)   They move to the left.
(b)   They move to the right.
(c)   They do not move.

### QUESTION 5*

This and the next question pertain to the following situation:

A ship of mass 150,000 kg and speed 8 m/s strikes a stationary iceberg of mass 10 times bigger than the mass of the ship. Assume that the forces exerted by the water on the ship and on the iceberg are negligible.

What is the resulting velocity of the iceberg if the ship and the iceberg are stuck together after the collision?

(a)   0.24 m/s
(b)   0.31 m/s
(c)   0.56 m/s
(d)   0.73 m/s
(e)   0.89 m/s

### QUESTION 6**

Let V be the answer to the previous problem. Suppose instead that the ship bounces off the iceberg with the same speed 8 m/s but in the opposite direction. What is now the resulting velocity of the iceberg?

(a)   larger than V
(b)   equal to V
(c)   smaller than V

### QUESTION 7*

This and the next question pertain to the following situation:

A 1800-kg car undergoes a collision during 0.25 s with an average force of 120,000 N.

By how much does the momentum of the car change?

(a)   400 kg-m/s
(b)   5000 kg-m/s
(c)   10,000 kg-m/s
(d)   20,000 kg-m/s
(e)   30,000 kg-m/s

### QUESTION 8*

This collision brings the car to a stop. What was the initial speed of the car?

(a)   3 m/s
(b)   7 m/s
(c)   13 m/s
(d)   17 m/s
(e)   22 m/s

### QUESTION 9*

This and the next question pertain to the following situation:

A uniform beam of length 3 meters and mass 90 kg is supported by two ropes, as shown below, and is in static equilibrium.

In which rope is the tension greater?

(a)   the left rope
(b)   the right rope
(c)   the tension is the same in each rope

### QUESTION 10*

What is the tension in the left rope?

(a)   220.5 N
(b)   250.1 N
(c)   290.6 N
(d)   314.2 N
(e)   365.0 N

### QUESTION 11**

This and the next question pertain to the following situation:

A uniform rod of length 4 m and of weight 5 N is supported at its extreme right end by a fulcrum as shown. A block of weight W = 10 N is sitting 1 m from the fulcrum. An upward force F is applied at the extreme left end.

What is the force F needed to keep the system in static equilibrium?

(a)   10 N
(b)   40 N
(c)   5 N
(d)   2.5 N
(e)   7.5 N

### QUESTION 12*

Now suppose that the fulcrum is moved directly under the block. Compared to your previous answer, the force needed to keep the system in static equilibrium will be

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

### QUESTION 13*

What is the angular velocity of the second hand of a clock?

### QUESTION 14*

This and the next two questions pertain to the following situation:

A wheel of radius 0.2 m starts from rest at t = 0 and rotates with constant angular acceleration about its axis to an angular velocity of 12 rad/s at t = 3 s.

What is the angular acceleration of the wheel?

### QUESTION 15*

How many revolutions does the wheel make during the period of acceleration?

(a)   2.9
(b)   3.7
(c)   1.5
(d)   8.6
(e)   6.9

### QUESTION 16*

At t = 1.5 s, what is the centripetal acceleration of a point on the rim of the wheel?

(a)   4 m/s2
(b)   15 m/s2
(c)   7.2 m/s2
(d)   36 m/s2
(e)   1.33 m/s2

### QUESTION 17*

This and the next question pertain to the following situation:

A child is pushing a toy chest across a rough floor with a constant force of 140 N directed at 30° below the horizontal. The mass of the child is 20 kg and the coefficient of friction between the chest and the floor is 0.46. The chest is pushed a distance of 2.0 m at constant speed.

What is the work done by the force of the child?

(a)   31 J
(b)   121.5 J
(c)   62 J
(d)   243 J
(e)   486 J

### QUESTION 18***

Suppose your answer to the preceding problem is W. The magnitude of the work done by friction is

(a)   greater than W.
(b)   equal to W.
(c)   less than W.

### QUESTION 19**

This and the next two questions pertain to the following situation:

A block of mass M = 3 kg with an initial speed of v0 = 15 m/s slides down a ramp of height h1 = 3 m above a horizontal surface, along the horizontal surface, then up a second ramp of height h2 = 5 m.

The net work done by gravity on the block between the first and second ramp is positive.

(T)   True
(F)   False

### QUESTION 20*

What is the speed of the block at the top of the second ramp, assuming all surfaces are frictionless?

(a)   9.2 m/s
(b)   11.5 m/s
(c)   18.2 m/s
(d)   5.9 m/s
(e)   13.6 m/s

### QUESTION 21**

Suppose instead that there is sliding friction between the block and the surfaces so that the speed of the block at the top of the second ramp is only 2 m/s. What is the magnitude of the work done by friction?

(a)   564 J
(b)   345 J
(c)   56 J
(d)   146 J
(e)   272 J

### QUESTION 22*

This and the next question pertain to the following situation:

A rope is attached to a block and a force is applied to pull the block up a rough incline at constant speed. The incline makes an angle of 30° with the horizontal. The tension in the rope is T=46 N, the mass of the block is M = 5 kg, and the block is pulled a distance D = 8 m up the incline.

What is the work done by gravity?

(a)   –196 J
(b)   –100 J
(c)   0 J
(d)   –172 J
(e)   –45 J

### QUESTION 23***

What is the work done by friction?

(a)   –196 J
(b)   –100 J
(c)   0 J
(d)   –172 J
(e)   –45 J

### QUESTION 24**

This and the next two questions pertain to the following situation:

Block A has a mass of 4 kg . It is released from rest and slides down a frictionless incline of height h above the floor. The incline makes an angle of 30° with the horizontal. Block B, which has a mass of 2 kg, is released from rest from the same height h above the floor and free-falls to the floor.

Which block has the largest kinetic energy when it reaches the floor?

(a)   Block A (the heavier block on the incline)
(b)   Block B (the lighter block in free-fall)
(c)   They both have the same kinetic energy.

### QUESTION 25**

Which block has the largest speed when it reaches the floor?

(a)   Block A (the heavier block on the incline)
(b)   Block B (the lighter block in free-fall)
(c)   They both have the same speed.

### QUESTION 26**

If both blocks are released at the same time, which one reaches the floor first?

(a)   Block A (the heavier block on the incline)
(b)   Block B (the lighter block in free-fall)
(c)   They both arrive at the same time.

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.