### Spring 2000 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 111. When the exam was given, the minimum "A" score was 99; the minimum "B" was 85; the minimum "C" was 72; the minimum "D" was 55. The mean was 87.7; the median was 93.

Click here to see the formula sheet that came with the exam. You should assume that the acceleration of gravity near the surface of the earth is 9.8 m/s2 downward, and ignore any effects due to air resistance.

### QUESTION 1*

This and the next question are about the following situation:

A car starts from rest and, moving with constant acceleration along a straight line, has a speed of 25 m/s after traveling 120 m.

What is the acceleration of the car?

(a)   1.25 m/s2
(b)   1.75 m/s2
(c)   2.20 m/s2
(d)   2.60 m/s2
(e)   3.20 m/s2

### QUESTION 2*

How long did the car take to travel 120 m?

(a)   5.4 s
(b)   6.2 s
(c)   7.3 s
(d)   9.6 s
(e)   11.3 s

### QUESTION 3**

This and the next question are about the following situation:

An object starts from rest and accelerates with constant acceleration. It travels a total distance D in the first 4 seconds? How far does it travel in the first 6 seconds?

(a)   1.50 D
(b)   2.00 D
(c)   2.25 D

### QUESTION 4**

How does the change in velocity between 3 and 4 seconds Dv34 compare with the change in velocity between 8 and 9 seconds Dv89?

(a)   Dv34 > Dv89
(b)   Dv34 = Dv89
(c)   Dv34 < Dv89

### QUESTION 5*

This and the next question are about the following situation:

An airplane on a humanitarian mission is flying horizontally at a speed of 120 m/s and an altitude of 2000 m when it drops a package of supplies.

How long does it take for the package to reach the ground?

(a)   23.5 s
(b)   18.1 s
(c)   20.2 s
(d)   15.9 s
(e)   25.4 s

### QUESTION 6**

What is the speed of the package when it hits the ground?

(a)   120 m/s
(b)   157 m/s
(c)   182 m/s
(d)   232 m/s
(e)   318 m/s

### QUESTION 7**

A rapidly flowing river runs from north to south. You want to drive a boat from the west bank to the east bank of the river in the shortest time possible. In which direction, with respect to the water, should you point the boat?

(a)   somewhat north of east
(b)   due east
(c)   somewhat south of east

### QUESTION 8*

Ball A is dropped with zero initial velocity from the top of a tall building. Simultaneously, ball B is projected horizontally with an initial speed of 20 m/s from the top of the same building. Which ball reaches the ground first?

(a)   ball A
(b)   ball B
(c)   They both reach the ground at the same time.

### QUESTION 9*

Suppose a box having a mass M sits on the floor of an elevator that is moving upward with constant velocity V. What is the magnitude of the normal force FN exerted by the elevator floor on the box?

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

### QUESTION 10*

Three forces act on an object as shown in the figure below. (F2 points along the x direction and F3 points along the -y direction). What is the magnitude of the net force acting on the object?

(a)   366 N
(b)   535 N
(c)   677 N
(d)   1224 N
(e)   2000 N

### QUESTION 11**

Consider the two situations depicted in the picture below. In case A, the person is pushing a sled with a force FA at an angle q. In case B, the person is pulling the same sled with a force FB acting at the same angle q. In both cases the sled is moving with the same constant velocity, and the coefficient of kinetic friction between the sled and the ground is the same. How does the magnitude of the force applied by the person compare in the two cases?

(a)   FA < FB
(b)   FA = FB
(c)   FA > FB

### QUESTION 12*

This and the next question are about the following situation:

A box of mass M slides down a frictionless inclined plane that makes an angle q with the horizontal.

What is the magnitude of the normal force acting on the box?

(a)   M g
(b)   M g cos(q)
(c)   M g sin(q)

### QUESTION 13**

What is the magnitude of the net force acting on the box?

(a)   M g
(b)   M g cos(q)
(c)   M g sin(q)

### QUESTION 14*

A 10 kg box is sliding with constant velocity down a ramp which makes an angle of 10° with the horizontal. What is the magnitude of the frictional force between the ramp and the box?

(a)   7 N
(b)   17 N
(c)   34 N
(d)   98 N
(e)   103 N

### QUESTION 15*

This and the next question are concerned with the same physical situation:

Suppose the cable of a crane is raising a box of mass M = 500 kg with an upward acceleration of 4 m/s2. What is the tension in the cable?

(a)   2450 N
(b)   6900 N
(c)   4530 N
(d)   9800 N
(e)   3340 N

### QUESTION 16*

If the tension in the cable exceeds 9000 N, it will break. What is the heaviest box the crane can lift with a constant upward velocity of 2 m/s?

(a)   918 kg
(b)   723 kg
(c)   1836 kg
(d)   1023 kg
(e)   602 kg

### QUESTION 17*

You are driving a 1400 kg car through a large flat parking lot. The coefficient of static friction between the tires and the pavement is ms = 0.25, and your speed is 30 m/s. What is the radius of the tightest turn you can make without the wheels of the car starting to slide on the pavement?

(a)   367 m
(b)   123 m
(c)   731 m
(d)   291 m
(e)   98 m

### QUESTION 18*

This and the next question are about the following situation:

Suppose you are driving in a car with a constant speed of V = 30 m/s through a valley whose bottom has the shape of a vertical circle of radius R = 90 m as shown in the figure. Your mass is 45 kg.

When the car is passing the bottom of the circular valley, what is the direction of its acceleration vector?

(a)   points forward (to the right)
(b)   points upward
(c)   points downward

### QUESTION 19*

As you drive past the bottom of the hill, what is the magnitude of the normal force FN exerted on you by the car seat?

(a)   FN = 891 N
(b)   FN = 734 N
(c)   FN = 563 N
(d)   FN = 398 N
(e)   FN = 223 N

### QUESTION 20*

Suppose the initial kinetic and potential energies of a system are 75 J and 250 J respectively, and that the final kinetic and potential energies of the same system are 300 J and -25 J respectively. The work done on the system by non-conservative forces in going from the initial to the final state was:

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

### QUESTION 21**

This and the next question are about the following situation:

Consider the following two ways of moving a box across a horizontal floor. In case 1, you are pushing on the box from an angle of 30° above horizontal, and in case 2 you are pulling on the box at an angle of 30° above horizontal (see pictures). The magnitudes of the applied force F, the coefficients of kinetic friction between the box and the floor, and the horizontal distances moved along the floor, are the same in both cases.

In which case is the magnitude of the work done by F on the box greatest?

(a)   case 1
(b)   case 2
(c)   The work done by F on the box is the same in both cases.

### QUESTION 22*

In which case is the magnitude of the work done by friction on the box greatest?

(a)   case 1
(b)   case 2
(c)   The work done by friction on the box is the same in both cases.

### QUESTION 23*

This and the next question are about the following situation:

Two balls are thrown horizontally from the roof of a 30 m tall building, hitting the level ground below (not necessarily at the same time). Ball A has a mass of 1 kg and is thrown with an initial speed of 4 m/s. Ball B has a mass of 4 kg, and is thrown with an initial speed VB.

If we want the balls to have the same speed when hitting the ground, which of the following statements best describes the initial speed of ball B:

(a)   VB = 4 m/s
(b)   VB > 4 m/s
(c)   VB < 4 m/s

### QUESTION 24*

If we want the kinetic energy of ball B to be 2000 J when it reaches the ground, what should its initial speed be?

(a)   VB = 9.8 m/s
(b)   VB = 12.5 m/s
(c)   VB = 18.9 m/s
(d)   VB = 20.3 m/s
(e)   VB = 25.2 m/s

### QUESTION 25**

A 5 kg box is pushed across a rough horizontal floor by a constant horizontal force F = 150 N, as shown below. The box starts at rest, and after having been pushed a distance D = 10 m it has a speed of 15 m/s.

What is the magnitude of the work done by friction on the box?

(a)   123 J
(b)   266 J
(c)   1500 J
(d)   937 J
(e)   562 J

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.