### Fall 2000 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 116. When the exam was given, the mean was 87.0; the median was 89. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

This and the next two questions relate to the same physical situation:

A disk of radius R is initially rotating with an angular velocity of 26 rad/s. At t = 0, brakes are applied resulting in a constant angular deceleration of magnitude 3.0 rad/s2.

How many revolutions does the disk make before coming to a stop?

(a)   8
(b)   12
(c)   18
(d)   22
(e)   29

### QUESTION 2**

Point A is located on the rim of the disk a distance R from the center. Point B is located a distance R/2 from the center of the disk. While the disk is slowing down, which point has the larger angular acceleration?

(a)   Point A.
(b)   Point B.
(c)   They both have the same angular acceleration.

### QUESTION 3**

Which point has the larger centripetal acceleration.

(a)   Point A.
(b)   Point B.
(c)   They both have the same centripetal acceleration.

### QUESTION 4*

This and the next question relate to the same physical situation:

A dragster starts from rest and accelerates down the track. Each tire has a radius of 0.35 m and rolls without slipping. After traveling a distance of 400 m, the angular speed of the wheels is 300 rad/s.

What is the linear speed of the dragster?

(a)   70 m/s
(b)   95 m/s
(c)   105 m/s
(d)   120 m/s
(e)   135 m/s

### QUESTION 5*

What is the magnitude of the angular acceleration?

### QUESTION 6**

This and the next question relate to the same physical situation:

A uniform board of length L and weight W is supported in two places: one on the extreme left end and the other 2L/3 from the left end.

What is the force exerted by the right support on the board?

(a)   3W/4
(b)   W/2
(c)   2W/3
(d)   W
(e)   3W/2

### QUESTION 7**

Now a box is placed on the extreme right end of the board. What is the maximum weight of the box such that the board does not tip?

(a)   W/4
(b)   W/2
(c)   W
(d)   2W
(e)   4W

### QUESTION 8**

Consider a thin rectangular board whose length L is larger than its width W, as shown in the figure. Three forces, A, B, and C of identical magnitude are applied at the corner in the plane of the board. Which force results in the largest torque about an axis perpendicular to the plane of plane of the board and passing through its center?

(a)
(b)
(c)

### QUESTION 9*

An irregular object is suspended vertically from the ceiling by a thin string and is in equilibrium, as shown in the picture above. Which of the three points A, B, and C best represents the location of the center of mass of the object?

(a)
(b)
(c)

### QUESTION 10**

A block of mass M = 1 kg is on a horizontal frictionless table and is attached to one end of a taut string of length L = 0.5 m. The block is spun around in a horizontal circle with a constant speed v = 3 m/s. A top view of the table and block is shown in the figure. The work done on the object by the string during half a revolution is

(a)   28 J
(b)   57 J
(c)   zero

### QUESTION 11*

A small ball of mass M is suspended from the end of a long string which is attached to the ceiling, forming a simple pendulum. The pendulum is drawn aside until the ball has risen 0.2 m, as shown in the figure. It is then released from rest. What is the speed of the ball after it has dropped by 0.1 m ?

(a)   1.4 m/s
(b)   2.8 m/s
(c)   0.7 m/s
(d)   3.0 m/s
(e)   zero

### QUESTION 12**

A box of mass M = 5 kg slides 10 meters with constant speed on a rough plane surface that is inclined at 30° to the horizontal. What is the magnitude of the work done by friction?

(a)   100 J
(b)   5 J
(c)   320 J
(d)   10 J
(e)   245 J

### QUESTION 13***

A force F is applied to block A of mass M over a distance D on a horizontal frictionless surface. The same force F is applied to block B of mass 2M over the same distance. Both blocks are initially at rest. Which block ends up with the larger kinetic energy?

(a)   Block A.
(b)   Block B.
(c)   Both blocks end up with the same kinetic energy.

### QUESTION 14*

This and the next question pertain to the same physical situation:

An object of mass M = 5 kg is moving horizontally in a straight line at a speed of 6 m/s. A force of 100 N is applied over a short period of time such that the speed of the object increases to 10 m/s.

The work done by the force is

(a)   100 J
(b)   15 J
(c)   5 J
(d)   260 J
(e)   160 J

### QUESTION 15*

What is the time period over which the force was applied?

(a)   10 s
(b)   0.35 s
(c)   0.15 s
(d)   0.2 s
(e)   5 s

### QUESTION 16**

A crane does a certain amount of work to lift a load from the ground to a height of 3 m in a time of 5 s. If it lifts it instead in 15 s, the work done would

(a)   increase.
(b)   decrease.
(c)   stay the same.

### QUESTION 17*

This and the next question pertain to the same physical situation:

An automobile of mass 1200 kg moving at 1.5 m/s collides with a lamp post and comes to rest. The collision takes 0.1 s.

What is the total impulse delivered to the automobile?

(a)   1100 kg-m/s
(b)   1200 kg-m/s
(c)   1600 kg-m/s
(d)   1800 kg-m/s
(e)   2400 kg-m/s

### QUESTION 18*

What is the mean acceleration of the car during the collision?

(a)   21 m/s2
(b)   19 m/s2
(c)   17 m/s2
(d)   15 m/s2
(e)   10 m/s2

### QUESTION 19*

Two objects of different mass have the same momentum. Which one has the larger kinetic energy?

(a)   the one with the larger mass
(b)   the one with the smaller mass
(c)   they both have the same kinetic energy

### QUESTION 20***

A car drives through a curve in the road at constant speed. Is the momentum of the car constant?

(a)   yes
(b)   no

### QUESTION 21*

This and the next question relate to the same physical situation:

One hockey puck of mass 0.2 kg moving at 20 m/s in the +x direction across a frictionless skating rink collides head-on with a second hockey puck of the same mass moving with the same speed in the -x direction.

Suppose the collision is elastic. What is the velocity of the second hockey puck after the collision?

(a)   0 m/s
(b)   -14.1 m/s
(c)   +14.1 m/s
(d)   -20 m/s
(e)   +20 m/s

### QUESTION 22*

Suppose instead that the collision is completely inelastic (i.e., the two pucks stick together after the collision). After the collision, the velocity of the two pucks is

(a)   in the +x direction.
(b)   in the -x direction.
(c)   zero.

### QUESTION 23*

A hockey player of mass M = 80 kg is at rest on a frictionless rink. He throws his hockey stick horizontally, and as a result he has a kinetic energy 0.01 times as much as the kinetic energy of the stick. What is the mass of the stick?

(a)   0.8 kg
(b)   0.95 kg
(c)   1 kg
(d)   1.1 kg
(e)   8 kg

### QUESTION 24***

Two blocks have identical mass M and speed v. One is moving in the –x direction, the other in the –y direction. The blocks collide and stick together. What is their energy after the collision?

(a)   Mv2
(b)   0.25 Mv2
(c)   0.5 Mv2
(d)   2Mv2
(e)   0

### QUESTION 25**

A block of mass M moving at speed v in the +x direction collides with a second block of mass 0.5 M moving at speed 2v in the –x direction. After the collision, the block of mass M has a speed v/3 in the –x direction. What is the momentum of the second block after the collision?

(a)   –Mv/4
(b)   +Mv/3
(c)   It depends on whether the collision is elastic or inelastic.

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.