Angular Motion Unit Exam Practice

Transcription

1 Angular Motion Unit Exam Practice Multiple Choice. Identify the choice that best completes the statement or answers the question. 1. If you whirl a tin can on the end of a string and the string suddenly breaks, the can will a. fly directly away from you. b. fly off, tangent to its circular path. c. fly directly toward you. d. spiral in toward your hand. e. spiral away from your hand. 2. People in the future may well live inside a rotating space structure that is more than 2 km in diameter. Inside the structure, people on the inside of the outer edge will experience 1 g while people halfway to the axis will experience a. 2 g. b. 1 g. c. g. d. g. e. 0 g. 3. As the rotational speed of a space habitat increases, the weight of people inside a. decreases. c. stays the same. 4. When a railroad train rounds a banked track, the centripetal force needed comes not from friction, but from the a. vertical component of the normal force. b. horizontal component of the normal force. c. normal force. 5. Stunt motorcyclist Biker Bob rides his bike inside a futuristic rotating space station a giant rotating donut-shaped structure in space. The normal support force feels like weight to him. As he rides his bike in the opposite direction to the station s rotation, the normal force a. remains unaffected. c. decreases. 6. Where is the center of gravity of a softball bat located? a. Exactly halfway along the bat b. In the thin handle c. In the more massive end of the bat 7. An object will fall over if its center of gravity is a. outside the object. b. too low. c. not over its area of support. d. too high. 8. The center of mass of the solar system a. varies as the planets move. b. is at the center of the sun. c. neither A nor B

2 9. An object thrown into the air with a spin rotates about its a. geometric center. b. center of gravity. c. edge. d. midpoint. e. none of the above 10. To turn a stubborn screw, it is best to use a screwdriver that has a _. a. yellow color b. wide handle c. long handle 11. As the rotational speed of a space habitat increases, the weight of people inside a. decreases. c. stays the same. 12. The resistance an object has to changes in its rotational state of motion is called rotational _. a. inertia b. momentum c. torque d. acceleration e. velocity 13. Which has more rotational inertia, a bicycle wheel or a solid disk of the same mass and diameter? a. The wheel. b. The disk. c. They both have the same rotational inertia. 14. Which has more rotational inertia, a girl running with her legs bent or the same girl running with her legs straight? a. With straight legs. b. With bent legs. c. Both have the same rotational inertia. 15. Any solid cylinder will roll down an incline with greater acceleration than any hollow cylinder if the _. a. diameter of the solid cylinder is large b. mass of the solid cylinder is small c. mass of the solid cylinder is large are necessary 16. A common thread spool rests on a flat table. You gently pull at an angle on a short piece of thread wrapped around the spool, which causes the spool to slide without rotating. With the thread at this angle, the lever arm is _. a. perpendicular to the applied force b. small, but not zero, and the torque is zero c. small and the torque is also small 17. A 3-kg ball is whirled on the end of a string that is 2 m long. The ball's linear speed is 4 m/s. What is its angular momentum? a. 2 kg m m/s b. 6 kg m m/s c. 8 kg m m/s d. 24 kg m m/s e. 48 kg m m/s

3 Essay. Use complete sentences to respond to each topic. You may use labeled sketches to supplement your response. 18. Which has more rotational inertia, a solid sphere of mass 100 kg and radius 50 cm or a solid cylinder of the same mass and radius? What is the rotational inertia of the sphere? Problem. Show all work including units and the correct sig figs with your answer. 19. A 5.5 kg rock rotates at the end of a 2.25 m rope that makes a 60-degree angle to the vertical (comprising a "conical pendulum"). Calculate 1) the tension on the rope, 2) the centripetal force, 3) the radius of the circlular path the rock makes, and 4) the tangential velocity of the rock. 20. A 85-kg boy and 55-kg girl sit at opposite ends of a balanced seesaw. The boy sits on 1.5 m from the fulcrum and the girl sits 2.0 m from the fulcrum. What is the mass of the seesaw? 21. What force must be applied perpendicular to the outer surface of a solid cylinder to generate an angular acceleration of 1.95 rad/s 2 around the symmetry axis? The cylinder has a mass of 29.3 kg, a radius of 0.25 m and a length of 2.0 m.

4 22. An gymnast summersaults at 0.9 revolutions per second in a layout position. When she summersaults in a tight tuck position she is rotating at 3.5 revolutions per second. If her initial moment of inertia was X what is her new moment of inertia as a fraction of X? 23. You sit at the outer rim of a Ferris wheel that rotates at 2 revolutions per minute (RPM). What would your rotational speed be if you were instead clinging to a position halfway from the center to the outer rim? If the radius of the Ferris wheel is 6.5 m, what is the tangential velocity at each position? 24. A vertical pole standing against a wall topples to the ground and the center of the pole has a speed of 13 m/s as it hits. With what speed does the far end of the pole hit the ground? 25. At the outer edge of a rotating space habitat, 130 m from its center, the rotational acceleration is g. What is the rotational acceleration at a distance of 65 m from the center of the habitat? 26. Suppose the torque produced by a wrench on a stubborn nut is 30 N m. If the lever arm is doubled with no change in force, what is the resulting torque? 27. Consider a long uniform wooden plank of weight W resting on a table. The left end of the plank can extend beyond the table without toppling as long as the CG of the plank rests on the table. If the CG extends beyond the table's edge, then a weight placed on its right end can prevent toppling. How much weight would prevent toppling if of the plank extended beyond the edge?

5