### Fall 2004 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 ***.

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 96. The exam period was 90 minutes; the mean score was 82.7; the median score was 87. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

This and the following question concern the same physical situation.

An 11 kg box is pushed on a horizontal floor at constant velocity. There is friction between the box and the floor. As shown in the figure, the force F = 25 N makes an angle θ = 20° with the horizontal.

What is the friction coefficient, μ, between the box and the floor?

(a)   μ = 0.00
(b)   μ = 0.10
(c)   μ = 0.20
(d)   μ = 0.30
(e)   μ = 0.40

### QUESTION 2**

If the angle θ was reduced to 10°, the speed of the box would

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

### QUESTION 3*

A satellite of unknown mass is in a circular orbit at a distance of 3 × 106 m above the surface of the earth (RE = 6.3 × 106 meters, ME = 6.0 × 1024 kg). The force on the satellite due to the earth is 116 N. What is the mass of the satellite?

(a)   m = 17 kg
(b)   m = 25 kg
(c)   m = 32 kg

### QUESTION 4*

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

A car starts from rest and moves with constant acceleration along a straight line. After traveling 150 m, it has a speed of 30 m/s.

What is the acceleration of the car?

(a)   0 m/s2
(b)   1 m/s2
(c)   2 m/s2
(d)   3 m/s2
(e)   4 m/s2

### QUESTION 5*

How long did the car take to travel 150 m?

(a)   10 s
(b)   20 s
(c)   30 s
(d)   40 s
(e)   50 s

### QUESTION 6*

If the car continues with this same, constant acceleration how far will it travel before reaching a speed of 60 m/s? That is, what is its displacement from the position at which it was stationary?

(a)   210 m
(b)   300 m
(c)   600 m

### QUESTION 7*

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

A centrifuge spins a 0.28 kg sample that is 0.15 m from its axis at a speed of 78.5 radians per second.

What is the speed of the sample in the centrifuge?

(a)   |v| = 6.8 m/s
(b)   |v| = 9.3 m/s
(c)   |v| = 11.8 m/s

### QUESTION 8**

What is the magnitude of the net force on the sample in the centrifuge?

(a)   |F| = 0
(b)   |F| = 168 N
(c)   |F| = 260 N
(d)   |F| = 283 N
(e)   |F| = 329 N

### QUESTION 9*

After being turned off, it takes the centrifuge 8 seconds to come to a complete stop.

What is the angular acceleration of the centrifuge as it slows down?

### QUESTION 10**

How many revolutions does the centrifuge make after it is turned off, before coming to a complete stop?

(a)   25
(b)   50
(c)   100

### QUESTION 11*

A box of mass M sits on the floor of an elevator that is moving downward 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 12*

This and the following question concern the same physical situation.

A 25 kg weight is suspended by two strings, as shown in the figure below. The left string makes an angle of 35 degrees with respect to the horizontal, and the right string makes an angle of 25 degrees with respect to the horizontal. The vertical component of the tension of the left hand string is TLy = 147 newtons.

What is the vertical component of the tension in the string on the right?

(a)   TRy =73.8 N
(b)   TRy =98.0 N
(c)   TRy =122.5 N

### QUESTION 13*

What is the magnitude of the horizontal tension in the string on the left?

(a)   TLx = 150 N
(b)   TLx = 210 N
(c)   TLx = 281 N

### QUESTION 14*

A 35 kg box is at rest on an incline as shown in the figure below. What is the friction force between the box and the incline if the angle α of the incline is 41°?

(a)   67 N
(b)   105 N
(c)   194 N
(d)   225 N
(e)   303 N

### QUESTION 15*

This and the following question concern the same physical situation.

A student who can swim with a speed of 2.6 m/s in still water wants to get to the other side of a 350 m wide river whose waters flows downstream at 1.1 m/s. If she swims across, starting at point A, in such a way that the time taken is the smallest possible,

How many seconds will it take her to cross the river?

(a)   350/1.1
(b)   350/2.6
(c)   350/3.7

### QUESTION 16*

How far (D) is she swept downstream of the point on the opposite bank directly across from her starting point?

(a)   148 m
(b)   202 m
(c)   259 m

### QUESTION 17*

This and the following question concern the same physical situation.

A massless rope connects block A to block B across a frictionless pulley as shown in the figure. Block B hangs vertically downwards and block A slides across a horizontal surface with a coefficient of kinetic friction, μk. Block A has a mass of 10 kg and block B has a mass of 6 kg. The tension, T, in the string is 48 N.

What is the acceleration of the blocks?

(a)   6.1 m/s2
(b)   3.7 m/s2
(c)   1.8 m/s2

### QUESTION 18*

What is the value of μk, the coefficient of kinetic friction between block A and the surface?

(a)   0.3
(b)   0.2
(c)   0.1

### QUESTION 19*

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

A stone is thrown vertically upward at 15 m/s. Neglect friction due to the air.

What is the stone’s velocity after 2 seconds?

(a)   4.6 m/s upward
(b)   2.2 m/s upward
(c)   0 m/s
(d)   2.2 m/s downward
(e)   4.6 m/s downward

### QUESTION 20*

How much time, t, does it take for the stone to get back to where it started?

(a)   t = 2.1 s
(b)   t = 3.1 s
(c)   t = 4.1 s
(d)   t = 5.1 s
(e)   t = 6.1 s

### QUESTION 21*

When the stone reaches its maximum height, its acceleration is

(a)   upwards.
(b)   zero.
(c)   downwards.

### QUESTION 22**

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

The quarterback of the football team throws the ball at a speed of 20 m/s at an angle of 25 degrees above horizontal as shown below. The ball is caught by the receiver at the same height above the ground from which it was thrown by the quarterback.

What is the speed |v| of the ball when it reaches its maximum height?

(a)   |v| = 0
(b)   |v| = 8.5 m/s
(c)   |v| = 18 m/s

### QUESTION 23*

What is the maximum height h the ball reaches above the point it was released?

(a)   h = 3.6 m
(b)   h = 7.8 m
(c)   h = 20 m

### QUESTION 24*

What is the distance S that the ball travels parallel to the ground before it is caught?

(a)   S = 27 m
(b)   S = 31 m
(c)   S = 34 m

### QUESTION 25*

What is the speed |v| of the ball just before it is caught?

(a)   |v| = 8.5 m/s
(b)   |v| = 18 m/s
(c)   |v| = 20 m/s

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.