### Fall 2009 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 125. The exam period was 90 minutes; the mean score was 83.6; the median score was 85. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1**

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

A physics 101 student weighs 600 N on Earth. She travels in her spaceship to mysterious planet X which has a radius rX that is twice the radius of Earth, rX = 2rE. On the surface of planet X, she finds that she weighs 300 N.

Relative to Earth's mass, mE, what is the mass of planet X?

(a)   0.25mE
(b)   0.5mE
(c)   1.0mE
(d)   2.0mE
(e)   4.0mE

### QUESTION 2*

How does the acceleration due to gravity on planet X, gX, compare to the acceleration due to gravity on Earth, gE?

(a)   gX > gE
(b)   gX = gE
(c)   gX < gE

### QUESTION 3***

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

Ralph is using the pulley system shown in the picture to hold a 45 kg mass stationary.

What is the force exerted by the ceiling?

(a)   222 N
(b)   442 N
(c)   662 N
(d)   882 N
(e)   1100 N

### QUESTION 4**

How does the force provided by Ralph's hand, fH, compare to the tension T in the rope?

(a)   fH = T / 3
(b)   fH = T
(c)   fH = 3 T

### QUESTION 5*

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

A physics book of mass 2 kg is sitting atop a table with coefficient of static friction μs = 0.4 and coefficient of kinetic friction μk = 0.3. A person is pushing the book as shown in the figure.

If the book is at rest, how hard can the person push on the book before it will start moving?

(a)   2.0 N
(b)   4.1 N
(c)   5.7 N
(d)   6.6 N
(e)   7.8 N

### QUESTION 6*

If the book has an acceleration of 1 m/s2, which of the following is a valid free body diagram for this situation? (Note: Ignore the length of the arrows; the direction is all that counts.)

(a)
(b)
(c)

### QUESTION 7*

A ball is tossed directly upward to some height above the ground and falls back down. Positive direction is upward. Which of the following is the correct description of the ball's velocity versus time?

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

### QUESTION 8***

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

Three boxes of equal mass, m, are connected to one another by strings as shown in the figure. They are pulled across a frictionless surface by tension T1.

Which of the three boxes has the largest net force acting on it?

(a)   box 1
(b)   box 2
(c)   box 3
(d)   boxes 1 and 3
(e)   All three boxes have the same net force acting on them.

### QUESTION 9**

Which of the following is a valid expression for the acceleration of box 1?

(a)   a = T1 / m
(b)   a = T1 / (2m)
(c)   a = T1 / (3m)
(d)   a = 2 T1 / m
(e)   a = 3 T1 / m

### QUESTION 10**

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

Professor Pitts pushes on a cart of mass 50 kg with a horizontal force Fpush. There is no friction. The cart has an acceleration of 5 m/s2.

Which one of the following statements is true?

(a)   By Newton's third law, the cart applies an equal and opposite force of magnitude Fpush on Professor Pitts.
(b)   The cart applies an opposite force on Professor Pitts, but it is smaller in magnitude than Fpush because of the acceleration force.
(c)   The force the cart applies on Professor Pitts is responsible for the acceleration of the cart.
(d)   The cart applies no force on Professor Pitts, because it is not pushing back on him.
(e)   The cart applies an opposite force on Professor Pitts and it is larger in magnitude than Fpush.

### QUESTION 11*

Starting from rest, the cart is observed to be travelling at a velocity of 5 m/s after 1 s. What is the magnitude of Fpush?

(a)   1 N
(b)   10 N
(c)   100 N
(d)   250 N
(e)   980 N

### QUESTION 12*

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

A block of mass m1 = 5 kg sits atop a frictionless incline which makes and angle θ = 25° as shown in the figure.

What is the acceleration of the block?

(a)   1.1 m/s2
(b)   2.1 m/s2
(c)   4.1 m/s2
(d)   9.8 m/s2
(e)   11.1 m/s2

### QUESTION 13*

The normal force provided by the incline on mass m1 and the weight of mass m1 have the same magnitude.

(T)   True
(F)   False

### QUESTION 14*

A second block of mass m2 = 10 kg is put on the incline next to mass m1 and the two masses are released at the same moment. Which mass wins the race to the bottom of the incline?

(a)   m1 wins.
(b)   m2 wins.
(c)   It's a tie: the two masses arrive at the same time.

### QUESTION 15**

This and the following question concern the same physical situation.

You are trying to shoot a monkey hanging on a tree branch using a toy cannon. You aim directly at the monkey and fire the cannon with a speed v and at an angle of 30° relative to the x direction. At the same time, the monkey lets go of the tree branch and fall toward the ground due to gravitational force. We ignore air resistance in this problem. The distance between the cannon and the tree is 50 m in the x direction.

The cannon ball hits the monkey 2 seconds later after the shot was fired. What was the initial speed of the cannon ball v?

(a)   28.9 m/s
(b)   25.3 m/s
(c)   22.1 m/s
(d)   20.0 m/s
(e)   18.9 m/s

### QUESTION 16*

What is the distance over which the monkey dropped before it got hit by the cannon ball?

(a)   9.8 m
(b)   19.6 m
(c)   25.4 m

### QUESTION 17*

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

There is a box with a total mass of 1 kg sitting on the floor of an elevator located in the middle of a vertical shaft. The elevator is free to move upward or downward. When the elevator is at rest, it takes a horizontal force of 4 N to make the box start to slide.

The elevator is now moving vertically (without friction). It takes 5 N of horizontal force to make the box start to slide. What can you say about the direction of elevator's motion?

(a)   It is going up.

(b)   It is going down.

(c)   Not enough information is given to determine in which direction the elevator is moving.

### QUESTION 18**

Now the elevator is accelerating vertically upward by 3 m/s2. What is the minimum horizontal force on the box required to make the box start to slide?

(a)   5.22 N
(b)   4.6 N
(c)   4 N
(d)   3.4 N
(e)   2.78 N

### QUESTION 19**

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

An airplane is flying due east relative to the air at a speed of 200 m/s.

The wind is blowing at 30 m/s toward the east relative to the ground. (With the wind), it takes 1.5 hours to fly from point A to point B, where point B is due east of point A. Under this condition, how long will it take to fly from point B to point A?

(a)   1.3 hours
(b)   2.0 hours
(c)   1.7 hours
(d)   1.85 hours
(e)   1.6 hours

### QUESTION 20**

Now the wind has changed its direction and is blowing towards the northeast direction. (See picture.) The wind has a speed of vwind = 30 m/s (as before). The airplane is flying due east relative to the air at a speed of vairplane = 200 m/s. What is the speed of the airplane relative to the ground?

(a)   173 m/s
(b)   180 m/s
(c)   202 m/s
(d)   222 m/s
(e)   231 m/s

### QUESTION 21***

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

You are flying on an airplane flying due east at a speed of 50 m/s and at an altitude of 1,000 m, and drop an apple of 0.1 kg in mass. Ignore air resistance for this problem. And there is no wind.

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

(a)   149 m/s
(b)   86 m/s
(c)   140 m/s
(d)   50 m/s
(e)   177 m/s

### QUESTION 22*

How long does it take the apple to reach the ground?

(a)   2.9 s
(b)   9.8 s
(c)   11.8 s
(d)   14.3 s
(e)   21.7 s

### QUESTION 23***

The following question refers to the drawing below, which is similar to that used in the labs. The cart and pulley are frictionless. The cart starts to move.

Which is the appropriate relationship between force pulling the cart (F), the mass of the cart (M), the mass of the weight (m), and acceleration of the cart (a)?

(a)   F = mg = Ma
(b)   F= (m+M)g = ma
(c)   F= (m+M)g = Ma
(d)   F = M= Ma
(e)   F= mMg/(m+M) = Ma

### QUESTION 24*

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

The diagram below is a graph of Mary walking on a runway. The detector is at zero position and velocity. The direction away from the detector is positive. Note: in reality, a person may not be able to exactly reproduce this.

Where is Mary accelerating?

(a)   B, D, F
(b)   A, C, E, G
(c)   D

### QUESTION 25*

What is Mary's velocity at the moment she changes direction?

(a)   infinity
(b)   negative infinity
(c)   0

### QUESTION 26*

What is the difference in Mary's motion comparing points B and D?

(a)   In B she is moving towards the detector while in D she is moving away from the detector.

(b)   There is no difference.

(c)   In B she is rapidly speeding up, till the point where she is moving away from the detector at constant speed, whereas in D she is rapidly changing direction until she is going at a constant speed walking towards the detector.

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.