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ame: ___________________________________________ Quiz 4--PHYS 201-1M--F13 Multiple Choice (30 pts) Identify the choice that best completes the statement or answers the question. 5. Consider a point on a spinning wheel rotating with rad α = 0 2 . Which of these statements best 1. Consider a child who is swinging. As she reaches the lowest point in her swing a. the tension is less than the weight b. the tension is greater than the weight c. the tension is equal to the centripetal force d. the tension equals mass*acceleration s describes the linear velocity of the point? a. the linear velocity is the same as the angular velocity b. the linear velocity is changing constantly c. the linear velocity equals α d. the linear velocity does not change 2. A rigid object is rotating with an angular speed ω< 0. The object is speeding up in its rotation. The angular acceleration is a. b. c. 6. What is the moment of inertia for this arrangement of particles that are attached to a central rod with massless rods? clockwise counterclockwise could be either CW or CCW 3. A disk is rotation at 3 rev/s. What is the rate of rotation in degrees/second? a. b. c. d. 0.008 degrees/second 1000 degrees/second 2 degrees/second 20 degrees/second 4. When travelling around a banked curve, which of these forces provides the centripetal force? a. b. c. d. I. Weight II. Normal force III. The speed of the car IV. Friction a. III & IV b. I c. II d. II & IV 1 18 kg m2 9 kg m2 16 kg m2 10 kg m2 8. Which of the following systems is not in rotational equilibrium? a. A figure skater spinning faster and faster on ice b. A ball spinning in place at a constant angular velocity c. A seesaw balanced motionless by two children d. A top spinning in place at a constant speed about its center of mass 7. This figure shows 3 levers of the same length. Each holds up a block of mass m. List the 3 levers in order of the force required to hold up the block, from greatest F to least F. 9. What are the units for moment of inertia? a. b. c. d. a. b. c. d. kg m kg m2 kg m/s N·m 3, 1, 2 2, 1, 3 1, 2, 3 1, 3, 2 10. These 4 wrenches have forces of the same magnitude applied to them in the direction of the arrow. Which experiences the greatest torque, and which experiences the least torque? a. b. (3) has the greatest torque. (4) has the least torque. (2) has the greatest torque. (4) has the least torque. c. d. (3) has the greatest torque. (2) has the least torque. (4) has the greatest torque. (1) has the least torque. 2 Problem 11. (10 pts) A merry-go-round rotates from rest with an angular acceleration of 1.50 rad/s 2. a) How long does it take to rotate through the first 2 revolutions? b) How much time is required to travel through the next 2 revolutions? (To solve for t requires solving a quadratic equation. Do not solve for t; just set up the appropriate equation with all numeric values.) 3 12. (15 pts) Consider these masses on a rod rotating about the fulcrum. The rod is 4 m long and has a mass of 3 kg. What is the initial angular acceleration of the system? (Treat the masses as point-size objects located at the ends of the rod. The rod is not massless.) 4 13. (15 pts) A collection of particles like this rotate around the axis as shown. A force of 3.0 N is applied to the 4.00 kg mass; the force is applied perpendicular to the rod that the mass is attached to. a)What is the angular speed of the system after 3.0 seconds? b) What is the linear speed of the 1.00 kg mass on the left at t=3.0 s? 5 15. (10 pts) A force 2i8 − 1j8 N acts on a moment arm of 3i8 − 2j8 N. What is the net torque that acts on the moment arm? 14. (10 pts) A boy swings a 2.0 kg stone in a vertical circle with a radius of 2.0 m. The string breaks when the stone rotates at 2 rad/s. a) What tension in the string will cause it to break? b) Where in its circular path does the string break: top, bottom, or side? . . 6 ID: A Quiz 4--PHYS 201-1M--F13 Answer Section MULTIPLE CHOICE 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: ANS: B A B D B A B A B A PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: PTS: 1 1 1 1 1 1 1 1 1 1 PROBLEM 11. ANS: . PTS: 1 12. ANS: . PTS: 1 13. ANS: . PTS: 1 14. ANS: . PTS: 1 15. ANS: . PTS: 1 1