PHYSICS 221 SPRING 2012

EXAM 1: February 16, 2012; 8:00pm—10:00pm

Name (printed): ______________________________________________ Recitation Instructor: _________________________ Section #_______ INSTRUCTIONS: This exam contains 25 multiple-choice questions plus 2 extra credit questions, each worth 3 points. Choose one answer only for each question. Choose the best answer to each question. Answer all questions. Allowed material: Before turning over this page, put away all materials except for pens, pencils, erasers, rulers and your calculator. There is a formula sheet attached at the end of the exam. Other copies of the formula sheet are not allowed. Calculator: In general, any calculator, including calculators that perform graphing, is permitted. Electronic devices that can store large amounts of text, data or equations (like laptops, palmtops, pocket computers, PDA or e-book readers) are NOT permitted. If you are unsure whether or not your calculator is allowed for the exam, ask your TA. How to fill in the bubble sheet:

Use a number 2 pencil. Do NOT use ink. If you did not bring a pencil, ask for one. Write and fill in the bubbles corresponding to: - Your last name, middle initial, and first name. - Your ID number (the middle 9 digits on your ISU card) - Special codes K to L are your recitation section. Always use two digits (e.g. 01, 09,

11, 13). Honors sections: H1 → 02; H2 → 13; H3 → 25. Please turn over your bubble sheet when you are not writing on it. If you need to change any entry, you must completely erase your previous entry. Also, circle your answers on this exam. Before handing in your exam, be sure that your answers on your bubble sheet are what you intend them to be. You may also copy down your answers on a piece of paper to take with you and compare with the posted answers. You may use the table at the end of the exam for this. When you are finished with the exam, place all exam materials, including the bubble sheet, and the exam itself, in your folder and return the folder to your recitation instructor. No cell phone calls allowed. Either turn off your cell phone or leave it at home. Anyone answering a cell phone must hand in their work; their exam is over.

Best of luck,

Drs. Soeren Prell and Kai-Ming Ho  

1. The angle between the vector !A = 3i ! 2 j ! 5k and the positive y axis, in

degrees, is closest to:

A) 19 B) 71 C) 90 D) 109 E) 161

   2. A rock is thrown directly upward from the edge of the roof of a building that is

34.9 meters tall. The rock misses the building on its way down, and is observed to strike the ground 4.00 seconds after being thrown. Neglect any effects of air resistance. With what speed was the rock thrown?

A) 6.4 m/s B) 12.1 m/s C) 3.6 m/s D) 8.7 m/s E) 10.9 m/s

3. The figure on the right shows the graph of

the position x as a function of time for an object moving in a straight line (along the x-axis). Which of the following graphs best describes the velocity along the x-axis as a function of time for this object?

4. A motorist traveling at a constant speed of 41.7 m/s in a 50 km/h speed zone

passes a police car. Immediately after the car passes, the police car starts off in pursuit. The police officer accelerates at 2 m/s2 up to a speed of 70 m/s, and then continues at this speed until she overtakes the speeding motorist. How long from the time she started does it take the police car to overtake the motorist? The motorist continues at a constant speed during this process.

A) 99 s B) 43 s C) 38 s D) 35 s E) 56 s

5. Three people are pushing a stalled car up a hill at constant velocity. The net

force on the car is

A) down the hill and greater than the weight of the car. B) up the hill and greater than the weight of the car. C) up the hill and equal to the weight of the car. D) down the hill and equal to the weight of the car. E) zero.

6. A girl throws a stone from a bridge. Consider the following ways she might

throw the stone. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown at an angle of 45o above horizontal. Case D: Thrown horizontally. The speed of the stone as it leaves her hand is the same in each case. In which case will the speed of the stone be greatest when it hits the ground below.

A) Case A B) Case B C) Case C D) Case D E) The speed will be the same in all cases.

7. For general projectile motion, when the projectile is at the highest point of its

trajectory

A) its acceleration is zero. B) its velocity and acceleration are both zero. C) the horizontal and vertical components of its velocity are zero. D) the horizontal component of its velocity is zero. E) its velocity is perpendicular to the acceleration.  

  8. A projectile is fired from point 0 at the edge of a

high cliff, with initial velocity components of v0x = 60.0 m/s and v0y = 175 m/s, as shown in the figure. The projectile rises and then falls into the sea at point P. The time of flight of the projectile is 40.0 s, and it experiences no appreciable air resistance in flight. The height of the cliff is closest to ….

A) 120 m B) 180 m C) 230 m D) 410 m E) 850 m

9. Two particles, A and B, are in uniform circular motion about a common

center. The acceleration of particle A is 5.5 times that of particle B. The period of particle B is 2.7 times the period of particle A. The ratio rA / rB of the radius of the motion of particle A to that of particle B is closest to

A) 2.0 B) 15 C) 4.1 D) 0.75 E) 0.49

10. An airplane flies between two points on the ground that are 500 km apart. The

destination is directly north of the origination of the flight. The plane flies with an air speed of 120 m/s. If a constant wind blows at 30.0 m/s due west during the flight, what direction must the plane fly relative to north to arrive at the destination?

A) 75.5° west of north B) 14.5° east of north C) 14.0° west of north D) 14.0° east of north E) 14.5° west of north

11. A man pushes against a rigid, immovable wall. Which of the following is the

most accurate statement concerning this situation?

A) If the man pushes on the wall with a force of 200N, we can be sure that the wall is pushing back with a force of exactly 200N on him.

B) The friction force on the man’s feet is directed to the left. C) Since the wall cannot move, it cannot exert any force on the man. D) The man cannot be in equilibrium since he is exerting a net force on the

wall. E) The man can never exert a force on the wall that exceeds his weight.

12. A cylinder slides down a frictionless

iceberg as shown in the figure. Which statement describes the magnitude of the cylinder’s velocity

v and the cylinder’s

acceleration a best while it is sliding down

the hill.

A) both v and

a remain constant.

B) both v and

a increase.

C) v decreases and

a increases.

D) v increases and

a decreases.

E) both v and

a decrease.

13. In the figure a block of mass M hangs in

equilibrium. The rope, which is fastened to the wall is horizontal and has a tension of 27N. The rope, which is fastened to the ceiling has a tension of 83N, and makes an angle θ with the ceiling. The angle θ is

A) 55 o B) 19 o C) 71 o D) 45 o E) 18 o

14. Dick and Jane stand on a platform of negligible weight, as shown in the figure. Dick weighs 500N and Jane weighs 400N. Jane is supporting some of her weight by holding a rope. Assume that all ropes and pulleys are ideal. What is the downward force Jane is exerting on the platform?

A) 0 B) 300 N C) 100 N D) 240 N E) 50 N

15. A worker is dragging a packing crate of mass 100kg across a rough floor

where the coefficient of kinetic friction is 0.40. He exerts a force sufficient to give the crate a positive acceleration. At what angle above the horizontal should his pulling force be directed in order to achieve the maximum acceleration?

A) 34.5 o B) 27.7 o C) 45.0 o D) 21.8 o E) 30.0 o

The next two questions pertain to the following scenario: “The Tornado” is a carnival ride that consists of a big vertical cylinder that rotates rapidly about its vertical axis with constant angular speed. As “The Tornado” rotates, the riders are pressed against the inside wall of the cylinder by the rotation. During the ride, the floor of the cylinder drops away. 16. The force preventing the riders from falling downward is …

A) the centripetal force. B) the normal force. C) the centrifugal force. D) the gravitational force. E) the friction force.

17. While “The Tornado” rotates, the net force acting on a rider …

A) points radially inward. B) points down. C) is zero. D) points in the direction of the riders velocity. E) points radially outward.

18. A 5.00-kg box slides 3.00 m across the floor before coming to rest. What is

the coefficient of kinetic friction between the floor and the box if the box had an initial speed of 3.00 m/s?

A) 0.183 B) 0.245 C) 0.153 D) 0.275 E) 0.214

19. A ball of mass 5.0 kg is suspended by two wires from

a horizontal arm that is attached to a vertical shaft, as shown in the figure. The shaft is in uniform rotation about its axis. The rate of rotation is adjusted until the tensions in the two wires are equal. At that speed, the radial acceleration of the ball is closest to

A) 6.9 m/s2 B) 7.9 m/s2 C) 5.9 m/s2 D) 9.9 m/s2 E) 4.9 m/s2

20. In order to do work on an object,

A) the object must move. B) the force doing the work must be directed perpendicular to the motion of the object. C) it is necessary that friction not be present. D) the applied force must be greater than the reaction force of the object. E) it is necessary that friction be present.

21. A system comprising blocks, a

massless frictionless pulley, a frictionless incline, and connecting massless ropes is shown. The 9-kg block accelerates downward when the system is released from rest. The tension in the rope connecting the 6-kg block and the 4-kg block is closest to

A) 39 N B) 30 N C) 36 N D) 42 N E) 33 N

F  m1   m2  

22. Which of the free-body diagrams below represents a block sliding down a

frictionless inclined surface?

23. Two blocks with masses m1 = 3.0 kg and m2 = 2.0 kg rest on a horizontal,

frictionless table. A horizontal force F is applied on block 1 from the left, as shown. The magnitude of the force exerted by block 1 on block 2 is 30 N. What is the magnitude of F?

A) 30 N B) 45 N C) 50 N D) 65 N E) 75 N

24. A conical pendulum made with a bead of

mass 4.0 kg and a 1.00 m long massless rope completes 1.2 turns every second. Determine the angle θ between the string and the vertical.

A) 40 o B) 50 o C) 60 o D) 70 o

E) 80 o 25. The work performed by an engine as a function of time for a process is given

by W = at3, where a = 2.4 J/s3. What is the instantaneous power output of the engine at t = 1.4 s?

A) 7 W B) 10 W C) 14 W D) 20 W E) 30 W

26. When a parachutist jumps from an airplane, she eventually reaches a

constant speed, called the terminal speed. Which statement describes the jump correctly?

A) Once the parachutist has reached terminal speed the force of air drag on her is zero. B) Once the parachutist has reached terminal speed the force of air drag on her is equal to her weight. C) Once the parachutist has reached terminal speed the net force on her is equal to her weight. D) When the parachutist jumps out of the plane her acceleration vector points upward. E) Airplanes cannot fly high enough for a parachutist to reach terminal speed.

27. A 4.00-kg box sits atop a 10.0-kg box on a horizontal table. The coefficient of

kinetic friction between the two boxes and between the lower box and the table is 0.600, while the coefficient of static friction between these same surfaces is 0.800. A horizontal pull to the right is exerted on the lower box, as shown in the figure, and the boxes move together. What is the friction force on the upper box?

A) 19.3 N to the left B) 31.4 N to the left C) 19.3 N to the right D) 31.4 N to the right E) 23.5 N to the right

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