### Fall 2010 Physics 101 Hour Exam 1(26 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 120. The exam period was 90 minutes; the mean score was 85.2; the median score was 89. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

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

A golf ball is hit upward at an angle θ from the horizontal and speed v = 40 m/s. It reaches a maximum height of 10 m as illustrated above. Assume the ballistic trajectory starts at ground level and ignore air resistance. Assume the shot is made on a wide, level field.

What is the initial angle θ ?

(a)   θ = 20.5°
(b)   θ= 46.4°
(c)   θ = 57.3°
(d)   θ = 70.2°
(e)   θ = 81.1°

### QUESTION 2*

How long is the ball in the air?

(a)   1.15 s
(b)   2.86 s
(c)   3.12 s
(d)   3.37 s
(e)   3.59 s

### QUESTION 3**

Suppose we are free to vary the angle θ (0 < θ ≤ 90°), but everything else remains the same. The ball will have the highest speed when it hits the ground if

(a)   θ = 90°
(b)   θ = 45°
(c)   All angles hit at the same speed.

### QUESTION 4*

Which one of the following most nearly is in free fall? Allow for air resistance.

(a)   A feather dropped from the top of Loomis Lab.
(b)   A bowling ball dropped from a height of 1 m.
(c)   A bungee jumper suspended from a taut bungee cord at the lowest point on her trajectory.

### QUESTION 5*

A man of mass 80 kg is in an elevator in the Burj Khalifa in Dubai (now the tallest building in the world). The elevator has a cruising speed of 8 m/s and reaches this speed at t = 4 s after starting from rest at t = 0 s. What is the man's apparent weight while the elevator is accelerating upward? Assume constant acceleration.

(a)   660 N
(b)   770 N
(c)   940 N
(d)   1010 N
(e)   Not enough information given.

### QUESTION 6**

Two boats A and B are moving on the surface of Lake Michigan. We will describe their motion using x and y coordinates; assume that x is to the east and y is to the north. Boat A has velocity vx = 5 m/s, vy = -1 m/s. Boat B has velocity vx = 4 m/s, vy = 1 m/s. What is their relative speed?

(a)   2.0 m/s
(b)   2.2 m/s
(c)   4.1 m/s
(d)   5.0 m/s
(e)   25 m/s

### QUESTION 7*

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

Two astronauts with masses m1 = 50 kg and m2 = 70 kg are floating freely in orbit, watching the sun set. The little one pushes the big one. During the push, which astronaut experiences the larger force?

(a)   the little one
(b)   the big one
(c)   They're the same.

### QUESTION 8*

Which astronaut experiences the larger acceleration?

(a)   the little one
(b)   the big one
(c)   They're the same.

### QUESTION 9*

Which one of the following must be moving at constant velocity?

(a)   a car moving down a straight road at constant speed
(b)   a car moving around a circular race track at constant speed
(c)   a car moving on a circular race track at varying speed.

### QUESTION 10*

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

A 30 kg boy is attached by a taut, ideal rope to a pole in the middle of an ice skating rink. The boy circles the pole at a speed v = 2.1 m/s and distance 3 m. What is the tension in the rope?

(a)   9 N
(b)   11 N
(c)   22 N
(d)   33 N
(e)   44 N

### QUESTION 11**

What is the boy's angular speed?

### QUESTION 12**

Suppose that the boy is actually moving with angular speed 0.5 rad/s, and begins to slow down at a rate of 0.01 rad/s2. How many times does he go around the pole before stopping?

(a)   once
(b)   twice
(c)   three times

### QUESTION 13**

You give the cart a push up a ramp, as shown in the following figure. The cart rolls up and then rolls back down the ramp. When the cart reaches the top, its acceleration is:

(a)   zero
(b)   downward
(c)   upward

### QUESTION 14***

A block is sliding up an incline, turns around, and slides back down. There is friction between the block and the incline. Which one of the following is true?

(a)   The magnitude of the acceleration is larger going up than going down.
(b)   The magnitude of the acceleration is larger going down than going up.
(c)   The magnitude of the acceleration is the same going up and going down.

### QUESTION 15**

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

A cart of mass M is on the frictionless horizontal table, and is connected to a mass m with an ideal string through a massless and frictionless pulley as shown in the figure at right.

When m is very large compared to M, what is the acceleration a of the cart?

(a)   a = 0
(b)   a is very large compared to g.
(c)   a is close to g.

### QUESTION 16***

When m = M, what is the acceleration a of the cart?

(a)   a = 0
(b)   a = g/2
(c)   a = g

### QUESTION 17**

There are three forces F1, F2 and F3 acting on the same mass, as illustrated below. The mass has zero acceleration. Using the coordinates shown in the figure, the force vectors in components read F1 = (0.2, 2.1) and F3 = (-4.1, -3.8) (in N). Find the magnitude of F2 .

(a)   2.8 N
(b)   3.3 N
(c)   3.8 N
(d)   4.3 N
(e)   4.7 N

### QUESTION 18**

Consider the two blocks connected with an ideal string through a massless and frictionless pulley as shown in the figure below. There is kinetic friction between the table and the block. The coefficient of kinetic friction between the block on the table and the table is μk .

Let a be the acceleration of block on the table to the right. The masses of the blocks are both equal to M. The tension in the string is T. Newton's second law tells us the following two equations.

Ma = T - μkMg

-Ma = T - Mg

Solving these simultaneous equations, obtain the acceleration a.

(a)   a = (1 - μk) g / 2
(b)   a = (1 + μk) g / 2
(c)   a = (1 - μk) g
(d)   a = (1 + μk) g
(e)   a = μk g

### QUESTION 19***

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

There is a block of mass M on the slope that makes an angle θ = 30° to the horizontal. The coefficient of static friction is 0.7.

The block is stationary on the slope. What is the magnitude of the friction force?

(a)   Mg cos 30°
(b)   0.7 Mg cos 30°
(c)   Mg sin 30°

### QUESTION 20**

How large can the angle θ be before the block starts to slip?

(a)   θ = 25°
(b)   θ = 35°
(c)   θ = 47°
(d)   θ = 55°
(e)   θ = 63°

### QUESTION 21*

This and the following question concern the same physical situation.

A block of mass 23 kg is under various forces and moves along the x-axis. The x-component of its velocity is plotted as the function of time shown below.

What is the largest magnitude of the net force acting on the block before t = 60 s ?

(a)   23 N
(b)   30 N
(c)   39 N
(d)   46 N
(e)   52 N

### QUESTION 22**

What is the average velocity of the block during these 60 seconds ?

(a)   3.3 m/s
(b)   5.0 m/s
(c)   6.7 m/s
(d)   8.3 m/s
(e)   10 m/s

### QUESTION 23**

This and the following question concern the same physical situation.

A ball is thrown upward with a certain initial velocity v0 from the top of a tower of height h at time t = 0. It reaches the highest point at time t = 2 seconds, and the ground at time t = 5 seconds.

What is the height of the tower?

(a)   7.5 m
(b)   11.5 m
(c)   16.5 m
(d)   20.5 m
(e)   24.5 m

### QUESTION 24*

Suppose the mass of the ball is doubled and the same experiment is repeated from the same tower with exactly the same initial velocity. How long does it take for the ball to reach the ground?

(a)   2 s
(b)   5 s
(c)   10 s

### QUESTION 25*

This and the following question concern the same physical situation.

There are three boxes on a horizontal surface as illustrated in the following figure. The masses of two of the boxes are known, as shown in the figure. A person pushes the leftmost box to the right with a force of 320 N. The boxes accelerate to the right at 8 m/s2.

What is the mass M of the middle box?

(a)   7 kg
(b)   9 kg
(c)   13 kg
(d)   17 kg
(e)   21 kg

### QUESTION 26**

What is the force exerted by the middle box on the leftmost box?

(a)   153 N
(b)   167 N
(c)   224 N
(d)   253 N
(e)   289 N

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.