### Spring 2010 Physics 101 Hour Exam 1(24 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 114. The exam period was 90 minutes; the mean score was 81.7; the median score was 83. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

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

The position vs time and velocity vs time diagrams for a block on a surface are shown at right.

What is the instantaneous velocity at t = 0.5 seconds?

(a)   31.4 m/s
(b)   -31.4 m/s
(c)   0 m/s
(d)   5 m/s
(e)   -5 m/s

### QUESTION 2*

What is the average velocity between t = 0 and t = 0.5 seconds?

(a)   31.4 m/s
(b)   -31.4 m/s
(c)   0 m/s
(d)   5 m/s
(e)   -5 m/s

### QUESTION 3*

What is the average acceleration between t = 0 and t = 0.5

(a)   126 m/s2
(b)   -126 m/s2
(c)   0 m/s2
(d)   31.4 m/s2
(e)   -31.4 m/s2

### QUESTION 4**

A man riding in an elevator measures his weight to be 750 N. His mass is 90 kg. If the y direction is up, then the y component of the acceleration of the elevator is

(a)   9.8 m/s2
(b)   -9.8 m/s2
(c)   0 m/s2
(d)   1.5 m/s2
(e)   -1.5 m/s2

### QUESTION 5*

A diver is in free fall from the moment she leaves a diving board until she hits the water 3 m below. She steps very, very slowly off the end of the board, so that her initial velocity is zero when she steps off the board. Her speed when she hits the water is

(a)   9.2 m/s
(b)   7.7 m/s
(c)   6.6 m/s
(d)   3.0 m/s
(e)   2.2 m/s

### QUESTION 6*

At the moment a car enters an intersection it is moving at 10 m/s. Because the driver sees the light turning yellow, she is accelerating forward at a constant 2 m/s2. It takes her 1.2 s to cross the intersection. How wide is the intersection?

(a)   5.1 m
(b)   7.9 m
(c)   11.7 m
(d)   12.9 m
(e)   13.4 m

### QUESTION 7**

This question and the following one concern the same physical situation.

A train is braking from an initial speed of 100 m/s. The train is braking hard, so the wheels are sliding over the rails. The coefficient of kinetic friction between the rail cars and the rails is μk = 0.1 . How long will it take the train to stop?

(a)   10 s
(b)   23 s
(c)   37 s
(d)   43 s
(e)   102 s

### QUESTION 8**

A train with 10 identical cars is moving forward and applies its brakes. Suppose the brakes fail on all but the first (leading) car. How does the magnitude of the force exerted by the first car on the second car F1-2 compare to the force exerted by the 9th car on the 10th car F9-10 ?

(a)   F1-2 = F9-10
(b)   F1-2 = 9 F9-10
(c)   F1-2 = 10 F9-10

### QUESTION 9*

This question and the following one concern the same physical situation.

Bob is standing on the floor of a cart that is moving horizontally at a constant speed v = 3 m/s. Ignore air resistance. The length of the cart L = 2 m and he is at the center point B of the cart.

Bob jumps straight up relative to the coordinate system of the moving cart with an initial speed of 4 m/s. What is the maximum distance between his foot and the cart floor? You may assume that his feet and other body parts move rigidly together.

(a)   0.35 m
(b)   0.57 m
(c)   0.64 m
(d)   0.82 m
(e)   0.97 m

### QUESTION 10*

When he lands on the cart floor, near which point does he land?

(a)   A
(b)   B
(c)   C

### QUESTION 11***

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

Suppose you are driving over a hill at constant speed v. The hill is roughly circular very close to and beyond the top, as shown in the figure.

If your mass is M, what relation does the magnitude of your apparent weight (i.e., the normal force F exerted on you by the car seat) have to the gravitational force on you as you drive over the top of the hill?

(a)   F = Mg + Mv2/R
(b)   F = Mg
(c)   F = Mg - Mv2/R

### QUESTION 12***

The car has not jumped off the ground at the top (the highest point) of the hill. Is it possible for the car to jump off the road subsequently before it reaches the foot of the hill? You may assume that the speed of the car is constant.

(a)   yes
(b)   no

### QUESTION 13**

If the speed of your car is 65 miles per hour your car takes off the ground at the top (the highest point) of the hill. This does not happen if the speed of your car is 60 miles per hour. What can you say about the radius of the hill R ? (1 mile = 1.6 km)

(a)   R is approximately 100 m.
(b)   R is approximately 80 m.
(c)   R is approximately 60 m.

### QUESTION 14**

This and the following question concern the same physical situation.

Audio CD players read the data on the disc at a constant linear speed and thus must vary the disc's rotational speed as the reading position moves from the inner edge to the outer edge. The radius of the innermost track is 25 mm and the rotational speed of the disk when the innermost track is read is 8 turns per second.

What is the required angular speed of the disk when the outermost track, whose radius is 58 mm, is read at the same rate as the innermost track?

### QUESTION 15**

You decide to stop listening to the music when the rotational speed is 40 rad/s, and the disk stops after 11 complete revolutions. What is the magnitude of the average angular acceleration?

### QUESTION 16***

Two cars are approaching a crossing as shown in the figure. The speed v1 of the car 1 is 15 m/s and the speed v2 of the second car is 25 m/s. The angle θ between the two roads is 54 degrees. What is the relative speed of the two cars?

(a)   28.2 m/s
(b)   32.5 m/s
(c)   34.1 m/s
(d)   35.9 m/s
(e)   40.0 m/s

### QUESTION 17*

If all the external forces on an object sum to zero, then which of the following is true?

(a)   The object must stand still (cannot be moving).
(b)   The object will have a constant velocity.
(c)   It is possible that the object may accelerate.

### QUESTION 18*

Two wooden blocks are hooked together and sit on a flat surface with friction. Which of the following statements regarding the forces exerted by each block on the other through the hooks is true?

(a)   If one block is pulling the other, then the pulling block exerts a greater force.
(b)   The forces are zero if the blocks are not moving.
(c)   The forces are equal in magnitude and opposite in direction.

### QUESTION 19**

The figure to the right represents a frictionless, massless pulley with two 5 kg blocks hanging from a massless string. The only forces acting on the blocks are gravity and the tension of the string. The total tension in the string is

(a)   approximately 49 N.
(b)   approximately 99 N.
(c)   approximately 198 N.
(d)   zero, because the masses are not moving.
(e)   none of the above

### QUESTION 20***

To the right is a diagram of a 4 kg weight hanging from a massless string. The weight is connected to a mass sitting on an inclined plane. There is no friction between the string and the inclined plane. The coefficient of static friction between the mass and the inclined plane is 0.35. What is the minimum mass of the block such that there is no movement of the mass up the inclined plane?

(a)   3 kg
(b)   5 kg
(c)   8 kg
(d)   10 kg
(e)   13 kg

### QUESTION 21*

A car is pulling a trailer that has a mass of 5000 kg. The trailer is connected to the car with a rope. The driver knows that the rope will break if a tension of 10000 N is applied. What is the largest possible acceleration of the car without breaking the rope? Assume no frictional forces on the trailer.

(a)   0.05 m/s2
(b)   0.2 m/s2
(c)   2 m/s2
(d)   20 m/s2
(e)   50 m/s2

### QUESTION 22*

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

A block of wood is pulled on a flat surface with a horizontal force F1 at steady velocity of V1. There is friction between the block and the surface. Now another block of wood (identical) is added on top of the original block. With what force F2 must one pull so that the stacked blocks travel at a constant velocity?

(a)   F2 = F1
(b)   F2 = 2F1
(c)   F2 = F1 / 2
(d)   One cannot tell without knowing the value of the frictional coefficient of kinetic friction.
(e)   One cannot pull a block at constant velocity on the surface with a constant force; it will always accelerate.

### QUESTION 23**

Is it possible to pull the original block at a constant velocity V2, which is different than V1, on the same surface with the force F1 of the above problem?

(a)   yes
(b)   no

### QUESTION 24*

Assume that the coefficient of static friction is larger than the coefficient of kinetic friction. Also assume that the block is pulled with the original force F1, and is traveling at the original velocity V1. The force F1 is removed, and the block comes to rest. If one again applies the same force F1 to the standing block, then

(a)   The block moves.
(b)   The block does not move.

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.