211 fa05 he 1a -questions

Physics 211. Exam 1 Fall 2005

Last Name: First Name: ID Discussion Section: Discussion TA Name:

Instructions—This is a closed book exam. You have ninety (90) minutes to complete it.

1. Use a #2 pencil. Do not use a mechanical pencil or pen. Darken each circle completely, but stay within the boundary. If you decide to change an answer, erase vigorously; the scanner sometimes registers incompletely erased marks as intended answers; this can adversely affect your grade. Light marks or marks extending outside the circle may be read improperly by the scanner. Be especially careful that your mark covers the center of its circle.

2. This Exam Booklet is Version A. Mark the A circle in the TEST FORM box near the middle of your answer sheet. DO THIS NOW!

3. Print your NETWORK ID in the spaces designated for that on the answer sheet; then mark the corresponding circle below each character. If there is a letter “o” in your NetID, be sure to mark the “o” circle and not the circle for the digit zero. If and only if there is a hyphen “-” in your NetID, mark the hyphen circle at the bottom of the column. (Do not mark the hyphen circles for any other reason.) When you have finished marking the circles corresponding to your NetID, check particularly that you have not marked two circles in any one of the columns.

4. Print YOUR LAST NAME in the designated spaces at the left side of the answer sheet, then mark the corresponding circle below each letter. Do the same for your FIRST NAME INITIAL.

5. Do not write in or mark the circles in any of the other boxes (STUDENT NUMBER, DATE, SECTION, SCORES, SPECIAL CODE).

6. Sign your name (DO NOT PRINT) on the STUDENT SIGNATURE line.

7. On the SECTION line, print your DISCUSSION SECTION. You need not fill in the COURSE or INSTRUCTOR lines.

Before starting work, check to make sure that your test booklet is complete. You should have 12 numbered pages including a Formula Sheet.

Academic Integrity—Giving assistance to or receiving assistance from another student or using unauthorized materials during a University Examination can be grounds for disciplinary action, up to and including dismissal from the University.

1 of 13 pages(28 problems)


Exam Grading Policy—

The exam is worth a total of 118 points, composed of three types of questions.

MC5: multiple-choice-five-answer questions, each worth 6 points. Partial credit will be granted as follows.

(a) If you mark only one answer and it is the correct answer, you earn 6 points. (b) If you mark two answers, one of which is the correct answer, you earn 3 points. (c) If you mark three answers, one of which is the correct answer, you earn 2 points.(d) If you mark no answers, or more than three, you earn 0 points.

MC3: multiple-choice-three-answer questions, each worth 3 points. No partial credit.

(a) If you mark only one answer and it is the correct answer, you earn 3 points. (b) If you mark a wrong answer, more than one answer or no answers, you earn 0 points.

TF: true-false questions, each worth 2 points. No partial credit.

(a) If you mark only one answer and it is the correct answer, you earn 2 points. (b) If you mark the wrong answer or neither answer, you earn 0 points.



1. Alice and Bill are standing at the top of a cliff of height H. Both throw a ball with initial speed v0. Alice throws her ball straight down and Bill throws his ball straight up. The speeds of the balls when they hit the ground are vA and vB respectively. Which of the following is true:

a. vA > vBb. vA = vBc. vA < vB

2. A girl is standing on a train that is moving west at 30 mph. She throws a ball horizontally. A boy on the ground observes the horizontal component of the velocity of the ball to be 5mph east. What is the horizontal component of the ball’s velocity with respect to the girl?

a. 25 mph eastb. 35 mph eastc. 40 mph east

3. Which of the following statements best describes the motion of an object that has a constant net force acting on it:

a. Its acceleration must be in the same direction as the force.b. Its velocity must be in the same direction as the force.c. Its velocity and its acceleration must both be in the same direction as the force.

4. Two blocks of masses m1 = 1kg and m2 = 2kg are connected by a massless spring with spring constant k = 100 N/m and placed on a frictionless plane inclined at 30. The larger block is connected to the wall via a weightless rope. What is the tension T in the rope?

a. 4.9 Nb. 7.6 Nc. 14.7 Nd. 19.6 Ne. 27.4 N


v0

vBA

H

Alice Billv0

g

k

T

30

m1

m2


The next two questions refer to the following situation:

A football is kicked across a level field. The ball spends 3 seconds in the air and lands 60 m from the point where it was kicked. (Ignore air resistance.)

5.

What is the speed of the ball at the top of its trajectory?

a. 0 m/sb. 5 m/sc. 10 m/sd. 15 m/se. 20 m/s

6. What is the maximum height H reached by the ball.

a. 9 mb. 10 mc. 11 md. 12 me. 13 m

7. A kid ties a rock to the end of a string and spins it in a circular path in the vertical plane. When the rock is at the bottom of the circle, which of the following is true about the tension T in the string:

a. T = mgb. T < mgc. T > mg


g

T

Hv0

v0x

v0y

60m

t = 0 t = 3 s

M M MT

9 N


8. The moon has mass MM = 7.3 x 1022 kg. It rotates about Earth in a circular orbit of radius RM = 3.84 x 108 m with period T = 27.3 days. The Earth has mass Me = 6.0 x 1024 kg and radius Re = 6.4x106 m. What is the centripetal acceleration of the moon due to its motion around Earth?

a. 0.0060 m/s2b. 0.00033 m/s2c. 0.31 m/s2d. 0.000051 m/s2e. 0.0027 m/s2

The next two questions are about the following situation:

Three identical masses M connected by massless ropes are being pulled to the right with a 9 N force across a horizontal, frictionless surface. The tension in the center rope is T.

9. If M = 3 kg, what is the tension in the center rope?

a. T = 3.0 Nb. T = 9.0 Nc. T = 6.0 Nd. T = 4.5 Ne. T = 7.0 N

10. If one were to double M for all three masses, and still pull to the right with a 9 N force, the tension in center string would

a. doubleb. triplec. stay the same


MM

Me

RM

Re


11. An inclined plane makes an angle with respect to horizontal. A box sits at rest on the ramp, held in place only by friction. The magnitude of the frictional force exerted by the ramp on the box is:

a. mg sin b. mg cos c. mg

The next two questions refer to the following situation.

A car of mass m= 2000 kg is driving with constant speed v= 40 m/s on a circular track of radius R = 22 m.

12. What is the magnitude of the acceleration of the car?

a. 1.0gb. 3.6gc. 4.4gd. 5.2ge. 7.4g

13. At the moment the car is pointing North, a passenger drops a rock out the window of the car. As viewed from above, what direction will the rock travel?

a. Northb. West c. Northeast


Top view

m

R

E

N

g

FA,H A

B


14. A 30 kg block (M1) is placed on a frictionless plane that inclines at a 30o angle with respect to the surface of Earth. This block is connected to another 20 kg block (M2) via a weightless rope over a frictionless, ideal pulley. The second block is hanging vertically, as shown in the figure. What is the tension of the rope?

a. 55.0 Nb. 92.4 Nc. 147.4 Nd. 176.6 Ne. 294.6 N


Blocks A and B accelerate on a frictionless horizontal surface while being pushed by your hand. Denote FA,H as the magnitude of the force on block A due to the hand, FA,B as the magnitude of the force on block A due to block B, and FB,A as the magnitude of the force on block B due to block A. Block B has 5 times the mass of block A.

15. Which statement correctly relates the magnitudes of FA,B and FB,A ?

a. FB,A = FA,Bb. FB,A > FA,Bc. FB,A < FA,B

16. What statement correctly relates the magnitude of the forces FA,H and FA,B?

a. FA,H = 2.4FA,Bb. FA,H = 1.2FA,Bc. FA,H = 1.5FA,Bd. FA,H = 3.0FA,Be. FA,H = 4.0FA,B


g

M2

M1

-2

-1

0

1

2

Fo

rce

(N

)

76543210

Time (seconds)

-4

0

4

Dis

pla

ce

me

nt

(cm

)

76543210

Time (seconds)



The two graphs below were obtained in Physics 211 Lab 2. A mass M is suspended vertically from the end of a spring. The other end of the spring is connected to a force probe which is rigidly connected to a support. A motion detector below the mass records the displacement of the mass. Assume that the force probe and motion detector read zero when the mass is hanging statically on the end of the spring.

When the mass is allowed to oscillate over the motion detector, the following graphs are obtained.

17. What is the force constant k of the spring?

a. k = 10 N/mb. k = 20 N/mc. k = 25 N/md. k = 35 N/me. k = 50 N/m

18. Keeping the mass the same and doubling the peak displacement, the peak force would

a. doubleb. stay the samec. not enough information



19. A truck of mass M = 1200 kg is moving up a hill with a constant acceleration a. A block of mass m = 3.3 kg is held in place by static friction, with coefficient of friction

between the block and truck bed. The hill is inclined at = 22 with respect to the horizontal. What is the maximum acceleration the truck can have before the block will slip?


The next two questions refer to the following situation:

A student can swim with a speed in still water. She swims across a river of width W and back. The river has a current of speed U, as shown in the figure. She swims in a path so that she travels directly from one side of the river to the other, such that her displacement is perpendicular to the shoreline. The path the student takes in the water is shown in the figure.

20. How long does it take the swimmer to get across the river and back?

a.

b.

c. d. 2W/V

e.

21. If she didn’t mind ending up downstream a bit the swimmer could get to the opposite bank and back in a shorter time than if she takes the path described above.


swimmer’s path

water W

g

M

a

= 22

m


a. Trueb. False




A rabbit runs across a parking lot on which a set of coordinate axis has been drawn. The coordinates of the rabbit’s position as a function of time t are given by:

and with t in seconds and x and y in meters.

22. At t = 15 s, what is the velocity of the rabbit?

a.

b.

c.

23. The rabbit is moving with constant acceleration.

a. Trueb. False


A block of mass m1 (labeled by U) is placed on top of a larger block of mass m2 (labeled by L). A man is trying to pull the blocks to the right via a spring (labeled by S) attached to the large block, but the blocks do not move.

24. The friction force between the large block and the ground is FL,G. What is the magnitude of the friction force between the large and small block?

a. 0b. FL,G m1/m2c. FL,G m1/(m1+m2)

25. Which one of the following pairs of forces is not an action-reaction pair in the figure?

a. the weight of mass m1 and the normal force of mass m2 pushing on mass m1.b. the spring pulling to the right on m2 and m2 pulling to the left on the spring.c. the weight of mass m2 and the gravitational force on the earth from mass m2.


m2

m1

S

U

FS

L


The next three questions refer to the following situation.

A box of mass m = 2 kg is being pulled by a horizontal string across the top of a second box having a mass of M = 5 kg. The kinetic coefficient of friction between the upper box and the lower box is = 0.2. There is no friction between the lower box and the floor. The upper box has a constant velocity, and the lower box starts out at rest and accelerates to the left.

26. Which of the following statements best describes the total force acting on the upper box (mass m):

a. The total force on the upper box points to the left.b. The total force on the upper box points to the right.c. The total force on the upper box is zero.

27. Which of the following is the free body diagram for the lower box (mass M): (a) (b) (c)

28. What is the magnitude of the acceleration of the lower box (mass M)?



=0.2

No frictionM=5kg

Tm=2kgT

N

Mg

mgmgT

Mg

N N

Mg

mgMg


Formula Sheet

Position: rVelocity: v = dr/dtAcceleration: a = dv/dt = d2r/dt2

Constant acceleration:v = v0 + atr = r0 + v0t + at2v2 = v02 + 2a(x-x0)

g = 9.81 m/s2 = 32.2 ft/s2

GN = 6.672 x 1011 N m2/kg2.

1 mile = 1.609 km

a = v2/r = 2rv = r = 2/T = 2f

Fnet = maFA,B = -FB,A

F = mg (gravity near earth’s surface)

F = - kxF = KN (kinetic friction)F SN (static friction)

Quadratic formula:

If then


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211 fa05 he 1a -questions

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