Fall 2001 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 117. When the exam was given, the mean was 98.4; the median was 102. Click here to see the formula sheet that came with the exam.

QUESTION 1*

A man lifts a bucket from a well at constant speed and does 20,000 J of work. If the well has a depth of 120 m, what is the mass of the bucket?

(a)   17 kg
(b)   9.8 kg
(c)   1 kg
(d)   20 kg
(e)   120 kg

QUESTION 2*

A car manufacturer claims that a super sports car of mass 800 kg will accelerate uniformly from rest to a speed of 35 m/s in 8 s. What is the net work on the car during this acceleration?

(a)   800,000 J
(b)   6,400,000 J
(c)   0 J
(d)   64,000 J
(e)   490,000 J

QUESTION 3*

This and the following question concern the same physical situation.

A 5.0 kg block is held at rest at the top of a rough incline that makes an angle of 30° with the horizontal. The total length of the incline is 2.5 m. The block is then released and slides at constant speed down the incline, reaching the bottom of the incline in 2 s. What is the work done by gravity on the block?

(a)   25 J
(b)   61 J
(c)   115 J
(d)   200 J
(e)   98 J

QUESTION 4**

Suppose your answer to the preceding problem is W. How much work is done by friction?

(a)   W
(b)   -W
(c)   no work is done by friction

QUESTION 5**

Two blocks, one of mass M and the other of mass 2M, are on a horizontal frictionless surface and are initially at rest. Then each block is acted upon by the same constant force F and for the same time interval D t. At the end of the time interval, which block has the larger kinetic energy?

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

QUESTION 6*

A block of mass M = 3 kg with an initial speed V slides down a frictionless hill of vertical height H = 3 m, along a horizontal frictionless surface, then up a second frictionless surface, reaching a maximum height H1 = 5 m. What was the initial speed V?

(a)   3.9 m/s
(b)   5.7 m/s
(c)   6.3 m/s
(d)   8.6 m/s
(e)   10.1 m/s

QUESTION 7*

Consider three identical balls are on the corners of a triangle. Specifically, the (x,y) coordinates of the three balls are (1,0), (-1,0), and (0,1), as shown in the drawing. The (x, y) coordinates of the center of mass of the three balls are:

(a)   (0, 0.33)
(b)   (0, 1)
(c)   (0.33,0)
(d)   (1,0)
(e)   (0,2)

QUESTION 8*

A girl of mass 50 kg jumps off the bow of a 75-kg canoe that is initially at rest. If her velocity is 2.5 m/s to the right, what is the speed of the canoe after she jumps?

(a)   3.34 m/s
(b)   2.5 m/s
(c)   0.0 m/s
(d)   1.67 m/s
(e)   5.0 m/s

QUESTION 9*

This and the following question concern the same physical situation.

A soccer ball of mass 0.45 kg is initially at rest when it is kicked by the kicker. The impulse imparted to the ball by the kicker is 9.0 N-s. What is the speed of the ball as it leaves the foot of the kicker?

(a)   25 m/s
(b)   18 m/s
(c)   20 m/s
(d)   5 m/s
(e)   9 m/s

QUESTION 10*

If the foot of the kicker is in contact with the ball for 0.005 s, what is the average force exerted by the foot on the ball?

(a)   1800 N
(b)   0.045 N
(c)   90 N

QUESTION 11*

This and the following question concern the same physical situation.

A 5.0-kg object moves to the right with a speed of 4.0 m/s and collides head-on with a 10-kg object, which is moving to the left with a speed of 3.0 m/s. The 10-kg object stops completely after the collision. You may assume that the only forces on the two objects are the forces they mutually exert on each other. With the positive direction to the right, the final velocity of the 5-kg object is:

(a)   8 m/s
(b)   6 m/s
(c)   – 3 m/s
(d)   – 2 m/s
(e)   – 4 m/s

QUESTION 12*

Suppose instead that the two objects stick together after colliding. In what direction does the combined system move after the collision?

(a)   To the left.
(b)   To the right.
(c)   The combined system is at rest.

QUESTION 13**

Block A of mass 2 kg has an initial velocity of 4 m/s. It collides and sticks to block B, which has a mass of 6 kg and is initially stationary. The two blocks then move together along a rough horizontal surface, eventually coming to a stop. Assuming that no net external forces act on the blocks during the collision, what is the magnitude of work done by friction in bringing the combined blocks to a stop?

(a)   2 J
(b)   3 J
(c)   4 J
(d)   5 J
(e)   6 J

QUESTION 14***

This and the following question concern the same physical situation.

A ball of mass M is released from rest a height H above the floor and collides elastically with the floor. What is the magnitude of the impulse exerted by the floor on the ball during the collision?

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

QUESTION 15**

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

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

QUESTION 16*

This and the following two questions concern the same physical situation.

A mobile consists of two boxes hanging from a uniform massless rod of length L=2 m. One box, whose mass is 3 kg, hangs from the left end of the rod. The other box, whose mass is 1 kg, hangs from the right end of the rod. The rod itself hangs by a wire attached to the ceiling (see the picture below, not necessarily shown to scale) and attached to the rod a distance d from the left end. The whole system is in static equilibrium and gravity points downward. What is the tension T in the wire?

(a)   22.8 N
(b)   39.2 N
(c)   56.2 N
(d)   74.1 N
(e)   94.5 N

QUESTION 17*

What is the distance d ?

(a)   1.5 m
(b)   1.0 m
(c)   0.5 m
(d)   0.25 m
(e)   0.75 m

QUESTION 18**

Suppose instead that the rod is not massless but is still uniform. In order to keep the system in equilibrium, the distance d of the wire from the left end of the rod must be:

(a)   larger
(b)   smaller
(c)   the same

QUESTION 19***

An irregularly shaped object of weight 2 N is suspended vertically from the ceiling by a string attached to a pivot point P. The center of mass (CM) is located a distance 0.4 m below the pivot point and 0.3 m to the left of the pivot point. The system is not in static equilibrium. Gravity points downward. What is the torque on the object about the pivot point due to gravity?

(a)   0.6 N-m
(b)   0.8 N-m
(c)   1.0 N-m

QUESTION 20**

This and the following three questions concern the same physical situation.

Two children ride on a merry-go-round of radius R = 3 m that is rotating with a constant angular velocity about its center. Child 1 is located on the rim of the merry-go-round and child 2 is located halfway between the center and the rim. Which child has the larger centripetal acceleration?

(a)   The one closer to the center.
(b)   The one further from the center.
(c)   They both have the same centripetal acceleration.

QUESTION 21*

In the preceding problem, suppose that the angular velocity is 25.0 rad/s. How many revolutions does the merry-go-round make in 15 s?

(a)   75
(b)   25
(c)   125
(d)   60
(e)   15

QUESTION 22*

Suppose that at t = 0, a brake is applied to the merry-go-round causing to decelerate with a constant angular acceleration of 5 rad/s2. How many revolutions does the merry-go-round make while coming to a stop?

(a)   10
(b)   13
(c)   20
(d)   28
(e)   35

QUESTION 23*

While the merry-go-round is slowing down, which of the two children has the larger magnitude of tangential acceleration?

(a)   The one closer to the center.
(b)   The one further from the center.
(c)   They both have the same tangential acceleration.

QUESTION 24*

As you drive down the road at 17 m/s, you press on the gas pedal and speed up with uniform acceleration of 1.12 m/s2 for 0.65 s. If the tires on your car have a radius of 0.33 m, what is their angular displacement (in radians) during this period of acceleration?

(a)   75
(b)   34
(c)   22
(d)   15
(e)   120

QUESTION 25*

An object initially at rest explodes into two equal pieces. Below are two possible pictures of the pieces after the explosion, where the arrows indicate the direction of the velocity of each piece. Which of these is possible?

(a)   only A
(b)   only B
(c)   both A and B

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.