Physics P201 D. Baxter/R. Heinz. EXAM #2 October 18, :00 9:00 PM INSTRUCTIONS

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1 Seat # Physics P201 D. Baxter/R. Heinz EXAM #2 October 18, :00 9:00 PM INSTRUCTIONS 1. Sit in SEAT # given above. 2. DO NOT OPEN THE EXAM UNTIL YOU ARE TOLD TO DO SO. 3. Print your name (last name first) and blacken in the letters on the answer sheet with a #2 pencil. 4. Print your student number (identification number) and blacken in the numbers on the answer sheet with a #2 pencil. 5. Use the fronts and backs of the question sheets for scratch work. Do not use any other scratch sheets. 6. This is a multiple choice exam. Blacken in the answer to each question on the answer sheet. Fill in one and only one answer to each question. 7. Keep your eyes on your own work. 8. You have two hours to complete the exam. When you finish, please show your picture ID as you turn in your answer sheet. Please leave quietly so others are not disturbed. 9. THERE ARE 24 QUESTIONS. PLEASE ANSWER ALL OF THEM. THERE IS NO PENALTY FOR GUESSING! You may use a calculator and two self-prepared sheets of formulas. You may also consult the appendices in the front and back of the book.

2 1. The unit for power is a watt. A watt is equivalent to: a. kg m 2 /s b. Js c. J/s d. kg ms 2 e. kw hr 2. Two blocks are released from the top of a building. One falls straight down while the other slides down a smooth ramp. One block is heavier than the other, but you don t know which is which. If all friction is ignored, which one is moving faster when it reaches the bottom? a. The block that went straight down. b. The block that went down the ramp. c. The lighter block. d. The heavier block. e. They both will have the same speed. 3. A 4.0 kg object moving at a speed of 3.0 m/s strikes a 2.0 kg object initially at rest. Immediately after this elastic collision, the 4.0 kg object has a velocity of 1.5 m/s directed 29 from its initial line of motion. What is the speed of the 2.0 kg object immediately after the collision? a. 3.7 m/s b. 3.2 m/s c. 2.7 m/s d. 2.2 m/s e. 1.7 m/s

3 4. A ball is held at a height H above a floor as shown in the diagram below. It is then released and falls to the floor. If air resistance can be ignored, which of the five graphs below the diagram correctly gives the mechanical energy (the sum of kinetic and potential energies) of the ball as a function of the altitude y of the ball? a. I. b. II. c. III. d. IV. e. V. 5. A 15.0 g bullet is shot horizontally into a 5085 g wooden block standing on a frictionless horizontal surface. The block, with the bullet in it, acquires a velocity of 1.80 m/s. Calculate the velocity of the bullet before striking the block. a. 512 m/s b. 612 m/s c. 712 m/s d. 812 m/s e. 912 m/s

4 6. A stationary object explodes, breaking into three pieces of masses m, m, and 3 m. The two pieces of mass m move off at right angles to each other with the same magnitude of momentum mv, as shown below. 3mv What is the magnitude of the velocity, v, of the piece having mass 3 m? = a. v 2V b. c. d. e. v = v = v = v = V 3 2V 3 V 3 V 2 7. A 2.0-kg object is acted upon by a single force in the x direction that has a time dependence shown in the graph. The momentum acquired by the object is: a. 16 N s b. 30 N s c. 32 N s d. 40 N s e. 48 N s

5 8. Two pucks are attached by a stretched spring and are initially held at rest on a frictionless surface, as shown. The pucks are then released simultaneously. If puck I has three times the mass of puck II, which of the following quantities is the same for both pucks as the spring pulls the two pucks toward each other? a. velocity b. kinetic energy c. acceleration d. speed e. the magnitude of the momentum 9. Sphere A has mass m and is moving with velocity v. It makes a head-on elastic collision with a stationary sphere B of mass 2m but the same radius as sphere A. After the collision the speed of sphere B is: a. 1 4 v b. 1 3 v c. 1 2 v d. 2 3 v e. 3 4 v

6 10. The bird perched on the swing in the figure has a mass of 50.0 g, and the base of the swing has a mass of 150 g. Assume that the swing and the bird are originally at rest, that the support wire is massless and that the bird achieves an initial horizontal velocity of 6.0 m/s by pushing off from the perch. If the base can swing freely (without friction) around the pivot, how high will the base of the swing rise above its original level? a. 5.4 cm b cm c cm d cm e cm 11. A ball of mass 0.4 kg is initially at rest on the ground. It is kicked and leaves the kicker's foot with a speed of 5.0 m/s in a direction 60 above the horizontal. The magnitude of the impulse I imparted by the ball to the foot is most nearly a. 0.5 N s b. 1.5 N s c. 2.0 N s d. 3.0 N s e. 4.0 N s 12. A potter s wheel moves from rest to an angular speed of 0.20 revolutions/second in 30.0 s. Find its angular acceleration. a..032 radians/second b..042 radians/second c..052 radians/second d..062 radians/second e..072 radians/second

7 13. A machine part rotates at an angular speed of 1.60 rad/s; its speed is then increased to 2.20 rad/s at an angular acceleration of rad/s 2.Findtheangle through which the part rotates during this period of uniform angular acceleration. a rad b rad c rad d rad e rad 14. An amusement park ride known as the cyclone consists of a large vertical cylinder that spins about the vertical axis. When it spins fast enough, any person inside will be held up against the wall. (The floor drops away after the cyclone has reached its top rotation speed.) Given: The coefficient ofstatic friction between the person and the wall µ = 0.503,themassofthepersonm = 60.0 kg, the radius of the cylinder R =8.00m. Find ω c, the critical angular speed below which a person will slide down the wall of the cylinder. a rad/s b rad/s c rad/s d rad/s e rad/s

8 15. Youandafriendareridingonaferriswheelwhichismovingwithconstant angular velocity. You, as a seeker of deep understanding, are sitting on a bathroom scale, wondering what will happen. Your friend observes 3 bathroom scale readings, on at the top, R t, one at the middle, R m, and one at the bottom, R b. The scale is always at the bottom of the square in the diagram representing the seat. The scale records the vertical component of force acting on its top surface. Which of the following is the correct relationship between R b, R t, R m? = > a. Rt Rb Rm b. Rt< Rm< Rb c. Rt= Rm= Rb d. Rt> Rm> Rb e. Rt= Rm< Rb 16. Tom has a mass of 70.0 kg and Sally has a mass of 50.0 kg. Tom and Sally are standing 20.0 m apart on a massless dance floor. Sally looks up and she sees Tom. She feels an attraction. If the attraction is gravitation, find its magnitude. Assume both are point masses. a. b. c. d. e N N N N N

9 17. An earth satellite remains in orbit at a distance of r = 10,000 km from the center 6 of the earth. The radius of the earth is m. What is its period? a. 24 hours b hours c hours d hours e hours 18. A rod on a horizontal tabletop is pivoted at one end and is free to rotate without friction about a vertical axis, as shown. A force F is applied at the other end, at an angle θ to the rod. If F were to be applied perpendicular to the rod with the same magnitude as in the figure, at what distance from the axis should it be applied in order to produce the same torque? a. L sin b. L tan c. L cos d. L e. 2L θ θ θ 19. Three objects are situated along the y axis as follows: a 3.0-kg object is at +2.5 m, a 2.5-kg object is at the origin, and a 4.0-kg object is at -.50 m. Where is the center of gravity of this system? = a. y.18 m b. y=.38 m c. y=.58 m d. y=.78 m e. y.98 m =

10 20. An automobile of mass 1200 kg is driven into a brick wall in a safety test. The bumper behaves like a Hooke s-law spring. It has an effective spring constant of N/m, and is observed to compress a distance of 3.1 cm as the car is brought to rest. What was the initial speed of the automobile? a. 5.1 m/s b. 6.3 m/s c. 7.5 m/s d. 8.7 m/s e. 9.9 m/s 21. and 22. Pete slides a 54.8 kg crate up a ramp at an angle of 20.0 by exerting a 325 N force parallel to the ramp. The crate moves at a constant speed. The coefficient of kinetic friction is N 0.86 m 21. How much work did Pete do when the crate was raised a vertical distance of m? a. 667 J b. 717 J c. 767 J d. 817 J e. 867 J 22. What was the work done by gravity while the crate was being raised? a. 462 J b. 512 J c. 562 J d. 612 J e. 662 J

11 23. A 0.80 kg block is released from rest and slides down a frictionless track that begins at h = 2.0 m above the horizontal, as shown in the figure. At the bottom of the track, where the surface is horizontal, the block strikes and sticks to a light spring with a spring constant of 3136 N/m. Find the maximum distance the spring is compressed. a. 2.0 cm b. 4.2 cm c. 6.1 cm d. 8.7 cm e cm 24. A 25 kg child on a massless 2.0 m long swing is released from rest when the swing supports make an angle of 30 with the vertical. The child (and swing) descends to her lowest position, where the speed of the child is 2.05 m/s. What is the work done by friction during this descent? a. -11 J b. -13 J c. -15 J d. -17 J e. -19 J