### Fall 2001 Physics 101 Hour Exam 1(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 110. When the exam was given, the mean was 89.1; the median was 92. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

Your car is traveling at 30 m/s when you press the brake. The car stops after 250 m. Assuming that the deceleration is constant, calculate the time to stop.

(a)   16.7 s
(b)   17.25 s
(c)   9.8 s
(d)   35.4 s
(e)   12.9 s

### QUESTION 2*

This and the following question concern the same physical situation.

A football player moves along a straight-line path to catch a ball thrown by the quarterback. The graph shows the speed as a function of time. Calculate the acceleration at 1 s, 2.5 s and 4 s.

 1 s 2.5 s 4 s a. 0.5 m/s2 0.0 m/s2 1.0 m/s2 b. 1.0 m/s2 0.0 m/s2 -2.0 m/s2 c. 2.0 m/s2 0.0 m/s2 -1.0 m/s2 d. 2.0 m/s2 1.0 m/s2 -2.0 m/s2 e. 2.0 m/s2 0.0 m/s2 -2.0 m/s2

(a)
(b)
(c)
(d)
(e)

### QUESTION 3*

How far does the player travel in the interval between t = 2 s and t = 3 s ?

(a)   0 m
(b)   2 m
(c)   4 m

### QUESTION 4*

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

A ball is thrown upward from the ground at an initial angle of 60° with respect to the horizontal and with an initial speed of 30 m/s. How high does the ball rise above the ground?

(a)   34.4 m
(b)   15.4 m
(c)   9.8 m
(d)   25.0 m
(e)   12.5 m

### QUESTION 5*

In the preceding question, what is the total time the ball is in the air before returning to ground level?

(a)   1.4 s
(b)   7.2 s
(c)   5.3 s
(d)   8.7 s
(e)   6.5 s

### QUESTION 6*

In the preceding question, suppose instead that the ball is initially thrown straight up with the same initial speed of 30 m/s. Compared to the preceding question, the total time the ball is in the air is now

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

### QUESTION 7*

This and the following questions concern the same physical situation.

A boat starts out on one bank of a river and heads directly across the river at a constant velocity of 5 m/s relative to the water. The river flows with a uniform velocity of 3 m/s. The river is 75 m wide. How far downstream from the original position does the boat cover while crossing to the opposite bank of the river

(a)   0 m
(b)   75 m
(c)   45 m
(d)   125 m
(e)   20 m

### QUESTION 8*

In the preceding question, which of the following answers is closest to the speed of the boat with respect to an observer on the bank of the river?

(a)   8 m/s
(b)   2 m/s
(c)   6 m/s

### QUESTION 9***

Ball A is released from rest from the top of a tall building. Ball B is projected horizontally from the top of the same building with a non-zero speed. Which ball has the higher speed as they hit the ground?

(a)   ball A
(b)   ball B
(c)   they have the same speed as they hit the ground

### QUESTION 10*

This and the following questions concern the same physical situation.

A 1200-kg car (which you may approximate as a point object) rounds a circular curve of radius R = 45 m. If the coefficient of static friction between the tires and the road is µs = 0.82, what is the maximum speed the car can have in the curve without the tires slipping?

(a)   25.2 m/s
(b)   11.8 m/s
(c)   15.8 m/s
(d)   19.0 m/s
(e)   30.6 m/s

### QUESTION 11**

Let your answer to the preceding problem be V. Suppose instead that the mass of the car is twice as large but that the radius of the curve is also twice as large. What is now the maximum speed the car can have in the curve without the tire slipping?

(a)   V
(b)   1.414 V
(c)   2 V

### QUESTION 12*

This and the following question concern the same physical situation.

A block of mass 4.0 kg is sitting on a horizontal frictionless surface and is pulled with a rope that makes an angle of 30° with the horizontal, as shown in the drawing below. The tension in the rope is 25 N. What is the acceleration of the block along the surface?

(a)   5.41 m/s2
(b)   7.81 m/s2
(c)   2.24 m/s2
(d)   3.54 m/s2
(e)   8.42 m/s2

### QUESTION 13**

In the preceding question, let the weight of the block be denoted by W. How does the normal force FN compare with W?

(a)   FN > W
(b)   FN = W
(c)   FN < W

### QUESTION 14**

A ball of mass M is suspended vertically from the end of a string. The other end of the string is attached to the ceiling of an elevator, as shown in the figure. The elevator is initially moving downward at constant speed. Just before reaching the bottom floor, the elevator slows down. As it is slowing down, the tension in the string will be

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

### QUESTION 15*

This and the following question concern the same physical situation.

Block A of mass 2 kg and block B of mass 4 kg are attached to each other by a string. The two blocks are sitting on a horizontal frictionless surface. Another string is attached to block B and the whole system is pulled to the right so that both blocks accelerate together, as shown in the figure. If the tension T is 15 N, as shown in the figure, what is the tension T1 in the string connecting the two blocks?

(a)   1 N
(b)   3 N
(c)   5 N
(d)   12 N
(e)   15 N

### QUESTION 16*

In the preceding question, suppose the order of the two blocks is reversed so that block A is in front and B is in back, with the same tension T = 15 N, as shown in the figure. Compared to the preceding problem, the tension T1 is now

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

### QUESTION 17**

This and the following question concern the same physical situation.

A block of mass M = 6 kg slides down an incline at constant velocity. The incline makes an angle of 40° with respect to the horizontal, as shown in the figure. What is the coefficient of kinetic friction between the block and the incline?

(a)   0.92
(b)   0.84
(c)   0.76
(d)   0.65
(e)   0.24

### QUESTION 18**

In the preceding problem, suppose the mass is doubled but both the angle and coefficient of friction remain the same. In this case, the block has a nonzero acceleration down the incline.

(T)   True
(F)   False

### QUESTION 19*

A truck is traveling at 7.5 m/s on a horizontal road. The brakes are applied and it skids to a stop in 2.0 s. The coefficient of kinetic friction between the tires and road is:

(a)   1.22
(b)   0.69
(c)   0.76
(d)   0.92
(e)   0.38

### QUESTION 20*

This and the following question concern the same physical situation.

A horizontal force of 10 N pushes a block against a vertical wall, holding it in place as shown in the figure. The coefficient of static friction between the block and the wall is µs = 0.59. How many different forces act on the block?

(a)   2
(b)   3
(c)   4

### QUESTION 21*

In the preceding problem, what is the maximum mass of the block such that it does not slip?

(a)   2.4 kg
(b)   9.8 kg
(c)   3.0 kg
(d)   0.6 kg
(e)   10 kg

### QUESTION 22*

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

Block A of mass 50 kg rests on a horizontal frictionless tabletop. A horizontal string is attached to A and passes over a massless, frictionless pulley and attaches to block B of mass 30 kg, as shown in the figure. Block A is held in place by hand so that the whole system is at rest. What is the tension in the string?

(a)   108 N
(b)   123 N
(c)   168 N
(d)   147 N
(e)   294 N

### QUESTION 23**

The system is then released and allowed to move freely. Compared to the preceding problem, the tension in the string is now:

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

### QUESTION 24*

Suppose instead that there is sliding friction between block A and the tabletop but that the system still moves freely. Compared to the preceding problem where the system moved freely without friction, the tension in the string is now:

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

### QUESTION 25**

Consider two identical satellites, each in circular orbit around the earth but at different distances from the center of the earth. Which satellite has the higher speed?

(a)   the one further from the center of the earth
(b)   the one closer to the center of the earth
(c)   they both have the same speed

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.