Exam 1 Fall 2010

8/6/2019 Exam 1 Fall 2010

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PHYSICS 221, FALL 2010

EXAM #1

WEDNESDAY, SEPTEMBER 29, 2010

Name (printed): ____________________________________________

Nine-digit ID Number: ____________________________________________

Section Number: ____________________________________________

Recitation Instructor: ____________________________________________

INSTRUCTIONS:

i. Put away all materials except for pens, pencils, erasers and your calculator. Turn off (not just

silence) any electronic communication devices that you have with you.

ii. Fill in your name, identification number, section number and recitation instructor above and

on the front of the multiple choice answer sheet using a number 2 pencil.

On the bubble sheet, print your LAST NAME, FIRST NAME, MI in the upper left-hand

corner, with a space between each. At the bottom left, put in your 9-digit ISU ID number.

Print your 2-digit recitation section number in the “special codes” columns K and L; e.g.

section 2 would be 02.

iii This exam contains 15 multiple choice problems worth 2 points each (problems 1-15), and 15multiple choice problems worth 4 points each (problems 16-30), for a total of 30 problems worth 90course points.

iv. In marking the multiple choice answer sheet use a soft number 2 pencil. Do NOT use ink. If youdid not bring a pencil, ask for one. Fill in the appropriate circles completely. If you need to changeany entry, you must completely erase your previous entry.

v. Carefully read each problem completely and its possible answers before beginning to work theproblem. For each problem, select one answer that is closest to the correct one.

vi. Please turn over or cover your answer sheet when you are not marking it.

vii. Before handing in your exam, make sure that your answers on your bubble sheet are the ones youintend them to be. Copy down your answers on a piece of unused scratch paper for comparisonwith the answer key to be posted later.

viii. When you are finished with the exam, please place all exam materials, including the answer sheet,the exam itself and scratch paper that you used for the exam, in your folder and return the folder toyour recitation instructor. Your exam will be returned to you in your next Tuesday recitation.

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Note: The unit vectors in the + x, + y, and + z directions of a right-handed Cartesian coordinate system

are i, j, and k , respectively. In this exam, assume that the magnitude of the acceleration due to

earth’s gravity at the surface of the earth is g = 9.80 m/s2.

Problems 1 through 15 are worth 2 points each

1. The speed of a car is 72.0 km/hour, which can also be expressed as ____ m/s.

A. 4 B. 8 C. 12 D. 16 E. 20

2. Two vectors!

F and!

G are shown in the figure. Which one of

the other five vectors shown is equal to!

G !

!

F ?

A.!

A

B.!

B

C.!

C

D.!

D

E.!

E

3. For the vectors in the figure in problem 2, which magnitude of the vector product is largest?

A.!

D !

!

E B.!

F !!

G C.!

D !

!

C D.!

A !

!

D E.!

B !

!

B

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4. A particle is moving along the x-axis. The x-component v x of its instantaneous velocity isplotted versus time t in the figure at the right.

The instantaneous acceleration of the particle attime t = 4.0 s is a x = ____ m/s2.

A. 2B. 1C. 0

D. −1

E. −2

5. For the particle with the velocity versus time plotted in the figure in problem 4, during what timeinterval(s) is the particle moving in the + x direction?

A. 0 s to 1 s and 3 s to 6 sB. 0 s to 2 s and 5 s to 6 sC. 0 s to 1 s onlyD. 0 s to 2 s only

E. 2 s to 5 s only

6. A cannon ball is launched from ground level at an angle of 60.0˚ above the horizontal with an initialspeed of 50.0 m/s. The speed of the cannon ball at the top of its trajectory is ____ m/s. Neglect anyinfluence of air friction.

A. 20 B. 25 C. 30 D. 35 E. 40

7. A circular disk is spinning in a clockwise direction with a particle attached toits circumference as shown. The angular velocity of the particle is pointed

____.

A. toward the right on the pageB. toward the left on the pageC. out of the pageD. into the pageE. upwards on the page

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8. Two balls are attached to a rigid disk that is rotating

counterclockwise at angular speed ω. Ball #1 is at a radius R

from the center of the disk and Ball #2 is at a radius of 2 R asshown in the figure. The speed of Ball #1 is v1. The speed of

Ball #2 is v2 = ____ . A. v1 / 2B. v1

C. 2 v1

D. 4 v1

E. 8 v1

9. Two blocks slide together toward the right on a horizontal

frictionless surface as shown. An external contact force!

F1

is applied to Block #1 that has mass m1. As the blocksaccelerate toward the right, Block #1 pushes on Block #2that has a mass m2 = m1/2. The contact force applied by

Block #1 on Block #2 is!

F2= ____ ,

A.!

F1

/ 3 B.!

F1

/ 2 C.!

F1

D. 2!

F1

E. 3!

F1

10. If a particle is moving with constant velocity, then ____ .

A. there are no forces applied to the particle.

B. a nonzero net force is applied to the particle.

C. the net force applied to the particle is zero.

D. a friction force on the particle must be present.

E. exactly one nonzero force is applied to the particle.

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11. An Atwood Machine consists of two blocks hanging by an idealmassless string that passes over an ideal massless frictionless pulley

as shown in the figure. If the masses of the two blocks are the same(m1 = m2 = m), then the tension in the string is T = ____ .

A. 4 mg B. 2 mg C. 3 mg / 2D. mg E. mg / 2

12. A roller coaster car is going over the top of a curve of radius R at

speed v as shown. The total mass of the car and the passenger is

M . The horizontal arrow shows the instantaneous velocity of thecar. The magnitude of the normal force exerted upwards by the

track on the car is ____ .

A. M g !v2

R

" # $

% & '

B. M g +v2

R

! " #

$ % &

C. M v2

R! g

" # $

% & '

D. Mg

E. Mv2/ R

13. Two constant horizontal forces!

F1and

!

F2, with

!

F1= !

!

F2, act on a block sliding on a horizontal table

as shown. When the block moves to the right from

initial position x = x i

to final position x = x f

as

shown, which one of the following answers is true

regarding the work W 1 done by!

F1

and the work W 2

done by!

F2?

A. W 2= !W

1

B. W 2=W

1

C. W 2=W

1/ 2

D. W 2 is positive

E. W 1 is negative

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14. A force with a magnitude of 3.00 N is exerted on one end of a spring (the other end is fixed in

position) in a direction parallel to the axis of the spring, and the spring becomes compressed by

1.50 cm. The spring constant of the spring is ____ N/m.

A. 100B. 200C. 300D. 400E. 500

15. A wood block of mass M slides in a straight line on a horizontal wood table with some initial speed.

The coefficient of kinetic friction of the block with the table is µk . After sliding a distance D, the

block comes to a stop. The initial kinetic energy of the block is ____ .

A. MgD B. µk MgD C. µk MgD / 2 D. MgD / 2 E. 2 MgD

Problems 16 through 30 are worth 4 points each

16. Two vectors!

A and!

B are given by!

A = (3.00 m) i + (4.00 m) j!

B = (3.00 m/s) i ! (4.00 m/s) j

The angle between

!

A and

!

B is ____ degrees.

A. 74 B. 86 C. 98 D. 102 E. 106

17. For the two vectors!

A and!

B in problem 16, their vector product is!

A !

!

B = _____.

A. (12.0 m2 /s) i + (12.0 m2 /s) j

B. (12.0 m2/s) i ! (12.0 m

2/s) j

C. !(24 m2/s) k

D. (24 m2/s) k

E. 24

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18. A particle is moving along the x-axis. The x-component v x of its instantaneous velocity is plottedversus time t in the figure at the right.

The change Δ x = x2 − x1 of the x-coordinate of the

particle between times t 1 = 1.0 s and t 2 = 5.0 s is____ m. (The change in a quantity is the final valueminus the initial value)

A. 4B. 2C. 0

D. −2

E. −4

19. A car is moving in a straight line in the positive x-direction with an initial speed of 20.0 m/s. The

brakes are applied and the acceleration of the car is then constant in time with a value a x = −2.00

m/s2 until the car stops. The time it takes the car to come to a stop after the brakes are applied is

____ s. Ignore any influence of air resistance.

A. 4 B. 6 C. 8 D. 10 E. 12

20. A ball is thrown straight up into the air from a height of 2.00 m above the ground with an initialspeed of 25.0 m/s. The height of the ball above the ground when the ball momentarily comes to astop is ____ m. Ignore any influence of air resistance.

A. 26 B. 30 C. 34 D. 38 E. 42

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21. A ball is launched horizontally at a speed v0 = 25.0 m/s from a

height h = 31.9 m above the ground as shown in the figure.

The speed of the ball just before it hits the ground is ____ m/s.Ignore any effects due to air friction.

A. 25B. 35C. 45D. 55 E. 65

22. A particle goes around in a circle of radius 3.00 m in the x- y plane. The angular position ! of the

particle with respect to the positive x-axis is given by ! = 5.60 rad " (2.50 rad/s2)t

2 , where t is the

time in seconds. The magnitude of the (total) acceleration of the particle at time t = 0.447 s is ____

m/s2.

A. 3 B. 12 C. 21 D. 30 E. 39

23. A bird flies 100 km directly north from Ames with respect to the ground. There is a wind presentwith a speed of 10.0 m/s that is blowing directly east with respect to the ground. If the speed of thebird with respect to the air is 15.0 m/s, it takes the bird ____ minutes to fly the 100 km.

A. 75 B. 100 C. 125 D. 150 E. 175

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24. Two forces!

F1and

!

F2

act on a 1.00 kg block with!

F1 = (3.00 N) i ! (4.00 N) j! (5.00 N) k . If the

acceleration of the block is!

a = (4.00 m/s2) i ! (8.00 m/s

2) k , the second force is

!

F2= _____ .

A. (7 N) i ! (4 N) j! (13 N) k

B. (4 N) i ! (8 N) k

C. (1 N) i + (4 N) j!

(3 N) k

D. (12 N) i ! (8 N) j! (29 N) k

E. (8 N) i + (8 N) j + (10 N) k

25. Two blocks are sitting at rest on a table, one on top of

the other as shown. Block #1 has mass m1 = 10.2 kg

and Block #2 has mass m2 = 5.1 kg. The magnitude of the contact force of the table on the bottom Block #1 is _____ N. (gravity is present)

A. 50B. 75C. 100D. 125E. 150

26. An Atwood Machine consists of two blocks hanging by an idealmassless string that passes over an ideal massless frictionless pulley asshown in the figure. The mass of Block #1 is m1 = 5.00 kg and themass of Block #2 is m2 = 15.00 kg. The magnitude of the accelerationof either block is ____ m/s2.

A. 9.8

B. 7.7C. 6.5D. 4.9E. 3.3

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27. A block of mass M = 5.00 kg hangs at rest from a massless ring by twomassless ropes 1 and 2 as shown. Rope 1 is horizontal and rope 2

makes an angle θ = 35˚ with the vertical. The tension in rope 2 is T 2 =

____ N.

A. 40B. 45C. 50D. 55E. 60

28. A 1500 kg car is going around a curve of radius 63.8 m on a horizontal flat (not banked) road. If the coefficient of static friction of the tires with the road is 1.00, the maximum speed at which thecar can go around the curve without sliding off the road is ____ m/s.

A. 25B. 22C. 19D. 16E. 13

29. A toy gun has an ideal massless spring in it with a spring constant of 400 N/m. When the gun is

cocked, the spring is compressed by 2.00 cm. Then when the gun is fired, the spring pushes on and

accelerates a 0.0100 kg rubber bullet, and the bullet leaves the gun at a speed of ____ m/s.

A. 4 B. 6 C. 8 D. 10 E. 12

30. A 2000 kg car accelerates in a straight line on a horizontal surface at a constant magnitude of

5.00 m/s2 starting from rest. When the car reaches a speed of 30.0 m/s, the instantaneous power

required to continue to accelerate the car at the same value is ____ kW.

A. 100 B. 150 C. 200 D. 250 E. 300

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Exam 1 Fall 2010