### Fall 2010 Physics 211 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 107. The exam period was 90 minutes; the mean score was 87.9; the median score was 92. Click here to see the formula sheet that came with the exam.

Unless otherwise stated, ignore air resistance and assume the acceleration of gravity is g = 9.81 m/s2 vertically downward.

### QUESTION 1*

This and the next three questions are about the following situation.

Three boxes are connected by massless strings and are resting on a frictionless table. Each box has a mass of 15 kg and the tension T1 in the right string is accelerating the boxes to the right at a rate of 2.5 m/s2.

What is the magnitude of the force T1?

(a)   37.5 N
(b)   75.0 N
(c)   113 N
(d)   157 N
(e)   192 N

### QUESTION 2*

If the boxes start from rest at t = 0. How far do they travel during the 3 seconds between time t = 1 seconds and t = 4 seconds?

(a)   11.3 m
(b)   18.8 m
(c)   20.0 m

### QUESTION 3*

What is the net horizontal force on box A?

(a)   37.5 N
(b)   75.0 N
(c)   113 N

### QUESTION 4*

What is the force on box B due to T3?

(a)   75.0 N to the left
(b)   37.5 N to the left
(c)   37.5 N to the right
(d)   75.0 N to the right
(e)   113 N to the right

### QUESTION 5*

This question and the next one are about the following situation.

A block of mass M is attached to the ceiling of an elevator by two strings.

Which one of the following equations applies to this system when the elevator is at rest?

(a)   T1 cosθ1 + T2 cosθ2 = 0
(b)   T1 sinθ1 - T2 sinθ2 = 0
(c)   T1 cosθ1 + T2 cosθ2 = Mg
(d)   T1 sinθ1 + T2 sinθ2 = Mg
(e)   T1 = T2

### QUESTION 6**

Let T1' be the tension in wire one when the elevator is moving upwards with a speed 8 m/s, but slowing down as it comes to a stop at the top floor. How does this tension compare to T1, the tension in the wire when the elevator is at rest.

(a)   T1' = T1
(b)   T1' < T1
(c)   T1' > T1

### QUESTION 7*

This question and the next two are about the following situation.

A 200 kg crate sits on the bed of a truck. The truck is accelerating to the right at 1.0 m/sec2. The static coefficient of friction between the crate and the truck bed is μs = 0.25. The kinetic coefficient is μk = 0.15. The crate does not slide relative to the truck bed.

The direction of the friction force on the crate from the truck is

(a)   to the left.
(b)   to the right.

### QUESTION 8**

The magnitude of the friction force on the crate is:

(a)   490 N
(b)   294 N
(c)   200 N
(d)   50 N
(e)   30 N

### QUESTION 9**

Now the truck accelerates at 8 m/sec2 (powerful truck!) and the crate slides back on the truck bed. What is the acceleration of the crate relative to the ground?

(a)   8 m/sec2 to the right
(b)   1.5 m/sec2 to the right
(c)   zero
(d)   1.5 m/sec2 to the left
(e)   8 m/sec2 to the left

### QUESTION 10*

This question and the next three are about the following situation.

A Ferris wheel has a radius of 8 meters, and spins counterclockwise with a constant angular velocity ω = 0.8 radians/second. (Cart B is going up at the instant shown.)

What is the speed of the cart A at the instant shown?

(a)   0
(b)   6.4 m/s
(c)   8.0 m/s

### QUESTION 11*

What is the x component of the acceleration of cart B at the instant shown?

(a)   -9.8 m/s2
(b)   -5.1 m/s2
(c)   0
(d)   5.1 m/s2
(e)   +9.8 m/s2

### QUESTION 12**

What is the y component of the acceleration of cart B at the instant shown?

(a)   -9.8 m/s2
(b)   -5.1 m/s2
(c)   0
(d)   5.1 m/s2
(e)   +9.8 m/s2

### QUESTION 13**

What is the maximum force the Ferris wheel will exert on 75 kg person as they go around the ride?

(a)   380 N
(b)   740 N
(c)   1120 N

### QUESTION 14*

This question and the next one are about the following situation.

Scientists want to place a 2800 kg satellite in a circular orbit around Mars. They plan to have the satellite orbit at a speed of 2100 m/s.

mmars = 6.5 × 1023 kg
rmars = 3.40 × 106 m
G = 6.67 × 10-11 N-m2/kg2

How far above the surface of mars will the satellite orbit?

(a)   3.4 × 106 m
(b)   5.1 × 106 m
(c)   6.4 × 106 m
(d)   7.3 × 106 m
(e)   8.5 × 106 m

### QUESTION 15**

Compare T1 the time needed to complete one orbit with the above parameters (v = 2100 m/s) to T2 the time needed to complete an orbit if instead it was placed in a circular orbit about mars with v = 4200 m/s.

(a)   T2 < (1/2) T1
(b)   T2 = (1/2) T1
(c)   T2 > (1/2) T1

### QUESTION 16*

This question and the next one are about the following situation.

A box is attached to a spring with a spring constant of 350 N/m on a frictionless incline that makes an angle of 30° with respect to horizontal as shown. The box is at rest when the spring is stretched 0.15 meters from its equilibrium length.

What is the mass of the box?

(a)   5.4 kg
(b)   6.2 kg
(c)   10.7 kg

### QUESTION 17*

The mass is released from the spring and slides down the incline. What is the speed of the block after it has moved a distance of 0.4 meters along the incline?

(a)   1.4 m/s
(b)   2.0 m/s
(c)   2.8 m/s

### QUESTION 18**

This and the next question are about the following situation.

An airplane travels with a velocity of 150 m/s due east with respect to the air. The air is moving with a speed of 50 m/s with respect to the ground at an angle of 45° north of east.

What is the speed of the plane with respect to the ground?

(a)   154 m/s
(b)   185 m/s
(c)   188 m/s

### QUESTION 19*

What is the heading of the plane with respect to the ground? (0° is due east, 90° is due north).

(a)   11° north of east
(b)   16° north of east
(c)   19° north of east

### QUESTION 20*

This and the next three questions are about the following situation.

A cannon ball is fired at a wall located 450 meters away (the diagram is not to scale). The initial horizontal component of the balls velocity is 90 m/s and its initial angle is 24°.

What is the initial speed of the ball?

(a)   75 m/s
(b)   99 m/s
(c)   114 m/s

### QUESTION 21*

How long does it take for the ball to reach the wall?

(a)   5.0 s
(b)   5.5 s
(c)   8.2 s

### QUESTION 22*

What is the maximum height the ball reaches?

(a)   82 m
(b)   164 m
(c)   246 m

### QUESTION 23*

How high above the ground is the ball when it reaches the wall?

(a)   34 m
(b)   78 m
(c)   128 m

### QUESTION 24*

This and the next two questions are about the following situation.

The graph below shows data obtained with the Physics 211 cart, track and motion detector. The position of a cart is shown as a function of time. The time interval between measurements is 0.05 s.

Which one of the following statements about the velocity of the cart is correct?

(a)   The velocity of the cart is positive from 0 s to 5 s.
(b)   The velocity of the cart is positive from 1 s to 4 s.
(c)   The velocity of the cart is positive only at 2.5 s.
(d)   The velocity of the cart is positive from 1 s to 2 s.
(e)   The velocity of the cart is positive from 3 s to 4 s.

### QUESTION 25**

Which one of the following statements about the acceleration of the cart is correct?

(a)   From 1 s to 4 s the acceleration of the cart goes from positive to negative.
(b)   From 1 s to 4 s the acceleration of the cart goes from negative to positive.
(c)   The acceleration of the cart does not change sign between 1 s and 4 s.

### QUESTION 26*

What is the average velocity of the cart between 1.5 s and 2.5 s?

(a)   1.0 m/s
(b)   0.8 m/s
(c)   -0.2 m/s
(d)   -0.6 m/s
(e)   -0.8 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.
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