practice ch 12 Test questions Multiple Choice Identify the letter of the choice that best completes the statement or answers the question. 1. The SI unit of force is the a. joule. c. meter. b. kilogram. d. newton. 2. Which of the following relationships is correct? a. 1 N = 1 kg c. 1 N = 1 kg m/s b. 1 N = 1 kg m d. 1 N = 1 kg m/s 2 3. When an unbalanced force acts on an object, a. the object s motion does not change. c. the weight of the object decreases. b. the object accelerates. d. the inertia of the object increases. 4. When a pair of balanced forces acts on an object, the net force that results is a. greater in size than both forces combined. c. equal in size to one of the forces. b. greater in size than one of the forces. d. equal to zero. 5. What kind of friction occurs as a fish swims through water? a. fluid c. sliding b. rolling d. static 6. As you push a cereal box across a tabletop, the sliding friction acting on the cereal box a. acts in the direction of motion. c. is usually greater than static friction. b. equals the weight of the box. d. acts in the direction opposite of motion. 7. The forces acting on a falling leaf are a. air resistance and fluid friction. c. gravity and static friction. b. gravity and air resistance. d. weight and rolling friction. 8. An open parachute increases air resistance of a falling sky diver by a. decreasing the weight of the diver. c. increasing the terminal velocity. b. increasing surface area. d. reducing fluid friction. Figure 12-1 9. Figure 12-1 shows the motion of three balls. The curved paths followed by balls B and C are examples of a. centripetal motion. c. linear motion. b. constant motion. d. projectile motion.
10. Projectile motion is caused by a. the downward force of gravity. b. an initial forward velocity. c. a final vertical velocity. d. the downward force of gravity and an initial forward velocity. 11. The property of matter that resists changes in motion is called a. friction. c. inertia. b. gravity. d. weight. 12. An orange might roll off your cafeteria tray when you stop suddenly because of a. the balanced forces acting on the orange. c. the friction forces acting on the orange. b. the centripetal force acting on the orange. d. the orange s inertia. 13. According to Newton s second law of motion, the acceleration of an object equals the net force acting on the object divided by the object s a. mass. c. velocity. b. momentum. d. weight. 14. If a force of 10 N is applied to an object with a mass of 1 kg, the object will accelerate at a. 0.1 m/s 2. c. 10 m/s 2. b. 9 m/s 2. d. 11 m/s 2. 15. Your weight equals your a. mass. b. mass divided by the net force acting on you. c. mass times the acceleration due to gravity. d. mass times your speed. 16. The acceleration due to gravity on the surface of Mars is about one-third the acceleration due to gravity on Earth s surface. The weight of a space probe on the surface of Mars is about a. nine times greater than its weight on Earth s surface. b. three times greater than its weight on Earth s surface. c. one-third its weight on Earth s surface. d. the same as its weight on Earth s surface. 17. Newton s third law of motion describes a. action and reaction forces. c. centripetal forces. b. balanced forces. d. net force. 18. In which of the following are action and reaction forces involved? a. when a tennis racket strikes a tennis ball c. when rowing a boat b. when stepping from a curb d. all of the above 19. The product of an object s mass and velocity is its a. centripetal force. c. net force. b. momentum. d. weight. 20. What is conserved when two objects collide in a closed system? a. acceleration c. speed b. momentum d. velocity 21. What is the momentum of a 50-kilogram ice skater gliding across the ice at a speed of 2 m/s? a. 25 c. 50 kg b. 48 kg m/s d. 100 kg m/s 22. What force is responsible for the repulsion between two positively-charged particles? a. centripetal c. gravitational b. electric d. nuclear
23. When opposite poles of two magnets are brought together, the poles a. attract each other. c. cancel each other. b. repel each other. d. cause a net force of zero. 24. Which universal force acts only on the protons and neutrons in a nucleus? a. electric c. magnetic b. gravitational d. strong nuclear 25. With which of the following is the weak nuclear force associated? a. lightning c. ocean tides b. nuclear decay d. static cling 26. Which of the following universal forces is the most effective over long distances? a. electric c. magnetic b. gravitational d. strong nuclear 27. As an astronaut travels far away from Earth, her weight a. decreases because gravity decreases. b. decreases because her mass decreases. c. increases because gravity increases. d. remains the same because her mass remains the same. 28. The gravitational force between two objects increases as mass a. decreases or distance decreases. c. increases or distance decreases. b. decreases or distance increases. d. increases or distance increases. 29. The force that keeps an object moving in a circle is called a. centripetal force. c. inertia. b. fluid friction. d. momentum. 30. The centripetal force acting on a satellite in orbit a. acts as an unbalanced force on the satellite. b. changes the direction of the satellite. c. is a center-directed force. d. all of the above Completion Complete each sentence or statement. 31. A push or pull is an example of a(an). 32. The type of force measured by a grocery store spring scale is. 33. The sum of all the forces acting on an object is called the _. 34. If the forces acting on an object produce a net force of zero, the forces are called _. 35. The force that opposes the motion of objects that touch as they move pass each other is called. 36. It usually takes more force to start an object sliding than it does to keep an object sliding because static friction is usually than sliding friction. 37. The two forces acting on a falling object are gravity and _. 38. When a falling object reaches terminal velocity, the net force acting on it is. 39. The drag force acting on an falling sky diver is also known as _.
40. The path of motion of a thrown javelin is an example of motion. 41. The tendency of an object to resist any change in its motion is called. 42. During a head-on auto collision, causes a passenger in the front seat to continue moving. 43. The acceleration of an object is equal to the net acting on the object divided by the object s. 44. The force of gravity acting on an object is the object s. 45. If a golf ball and bowling ball are rolling at the same speed, the ball has greater momentum. 46. When you push on a wall, the pushes back on you. 47. In a closed system, the loss of momentum of one object the gain in momentum of another object. 48. The observation that a charged object can attract or repel other charged objects led scientists to conclude that there are types of charges. 49. The universal force that is most effective over the longest distances is. 50. The centripetal force acting on the moon continuously changes the of the moon s motion. Short Answer 51. How can an arrow be used to represent the size and direction of a force? 52. What happens to the magnitude of the fluid friction acting on a submarine as the submarine s speed increases? Figure 12-1 53. Figure 12-1 shows the paths followed by three balls. Each ball started moving at the same time. Ball A was dropped and balls B and C were thrown sideways. Compare the times for each ball to reach the ground. 54. What is the direction of the net force on a falling sky diver before she reaches terminal velocity? After she is falling at terminal velocity? 55. How can you double the acceleration of an object if you cannot alter the object s mass?
56. During a collision, a seat belt slows the speed of a crash-test dummy. What is the direction of the net force exerted by the seat belt compared to the direction of the dummy s motion? 57. How are the size and direction of action-reaction forces are related? 58. Why don t action-reaction forces cancel each other? 59. What law states that if no net force acts on a system, then the total momentum of the system does not change? 60. A billiard ball with a momentum of 20 kg m/s strikes a second ball at rest and comes to a complete stop. What is the change in momentum of the second ball? 61. Compare the speed of a moving golf ball with the speed of a moving bowling ball if both balls have the same amount of momentum. 62. Electric force and magnetic force are the only forces that can both do what? 63. One end of a bar magnet attracts one end of a second bar magnet. What will happen if the second bar magnet is reversed? 64. Which of the universal forces acts only on protons and neutrons in the nucleus of an atom? 65. What is the primary cause of Earth s ocean tides? Problem 66. A crane exerts a net force of 900 N upward on a 750-kilogram car as the crane starts to lift the car from the deck of a cargo ship. What is the acceleration of the car during this time? Show your work. 67. The mass of a newborn baby is 4.2 kilograms. What is the baby s weight? (The acceleration due to gravity at Earth s surface is 9.8 m/s 2.) Show your work. 68. A small 32-kilogram canoe broke free of its dock and is now floating downriver at a speed of 2.5 m/s. What is the canoe s momentum? Show your work. 69. A small engine causes a 0.20-kg model airplane to accelerate at a rate of 12 m/s 2. What is the net force on the model airplane? Show your work. Essay 70. Why does a biker have to pedal harder to travel at a constant speed into the wind on a windy day compared to traveling on the same road at the same speed on a calm day? Other USING SCIENCE SKILLS
Figure 12-2 71. Interpreting Graphics In Figure 12-2, what is the direction of the centripetal force acting on the satellite at this location in its orbit? 72. Predicting What happens to the size of the centripetal force due to gravity acting on the satellite in Figure 12-2 if the satellite moves farther from Earth? 73. Applying Concepts The centripetal force acting on the satellite in Figure 12-2 is one of a pair of action-reaction forces. On what object is the other force in the pair acting? 74. Interpreting Graphics In Figure 12-2, what property of the satellite tends to keep it moving along through its orbit? 75. Inferring As shown in Figure 12-2, what is the direction of the fluid friction acting on the satellite as it moves through the outer layer of Earth s atmosphere? Figure 12-3
76. Interpreting Graphics In Figure 12-3, what is the momentum of each skater at Time 1? 77. Comparing and Contrasting In Figure 12-3, compare the size and direction of the momentums of both skaters immediately after the push shown at Time 2. 78. Interpreting Graphics In Figure 12-3, describe the motion of Skater B after Skater A pushes her. 79. Applying Concepts In Figure 12-3, if Skater A is pushing Skater B, why does Skater A move? 80. Applying Concepts Suppose that the skaters repeat the demonstration in Figure 12-3 again. This time Skater B is holding a 10-kilogram mass. If Skater A pushes exactly as he did the first time, will Skater A s motion be different this time? Explain your answer.
practice ch 12 Test questions Answer Section MULTIPLE CHOICE 1. ANS: D DIF: L1 OBJ: 12.1.1 2. ANS: D DIF: L2 OBJ: 12.1.1 3. ANS: B DIF: L1 OBJ: 12.1.2 4. ANS: D DIF: L2 OBJ: 12.1.2 5. ANS: A DIF: L1 OBJ: 12.1.3 6. ANS: D DIF: L2 OBJ: 12.1.3 7. ANS: B DIF: L1 OBJ: 12.1.4 8. ANS: B DIF: L2 OBJ: 12.1.4 9. ANS: D DIF: L1 OBJ: 12.1.5 10. ANS: D DIF: L2 OBJ: 12.1.5 11. ANS: C DIF: L1 OBJ: 12.2.1 12. ANS: D DIF: L2 OBJ: 12.2.1 13. ANS: A DIF: L1 OBJ: 12.2.2 14. ANS: C DIF: L2 OBJ: 12.2.2 15. ANS: C DIF: L1 OBJ: 12.2.3 16. ANS: C DIF: L2 OBJ: 12.2.3 17. ANS: A DIF: L1 OBJ: 12.3.1 18. ANS: D DIF: L2 OBJ: 12.3.1 19. ANS: B DIF: L1 OBJ: 12.3.2 20. ANS: B DIF: L1 OBJ: 12.3.2 21. ANS: D DIF: L2 OBJ: 12.3.2 22. ANS: B DIF: L1 OBJ: 12.4.1 23. ANS: A DIF: L2 OBJ: 12.4.1 24. ANS: D DIF: L1 OBJ: 12.4.2 25. ANS: B DIF: L2 OBJ: 12.4.2 26. ANS: B DIF: L1 OBJ: 12.4.3 27. ANS: A DIF: L1 OBJ: 12.4.3 28. ANS: C DIF: L2 OBJ: 12.4.3 29. ANS: A DIF: L1 OBJ: 12.4.4 30. ANS: D DIF: L2 OBJ: 12.4.4 COMPLETION 31. ANS: force DIF: L1 OBJ: 12.1.1 32. ANS: weight DIF: L2 OBJ: 12.1.1 33. ANS: net force
DIF: L1 OBJ: 12.1.2 34. ANS: balanced forces balanced DIF: L2 OBJ: 12.1.2 35. ANS: friction DIF: L1 OBJ: 12.1.3 36. ANS: greater larger DIF: L2 OBJ: 12.1.3 37. ANS: air resistance drag DIF: L1 OBJ: 12.1.4 38. ANS: zero DIF: L2 OBJ: 12.1.4 39. ANS: air resistance DIF: L2 OBJ: 12.1.4 40. ANS: projectile DIF: L1 OBJ: 12.1.5 41. ANS: inertia DIF: L1 OBJ: 12.2.1 42. ANS: inertia, forward DIF: L2 OBJ: 12.2.1 43. ANS: force, mass DIF: L1 OBJ: 12.2.2 44. ANS: weight DIF: L1 OBJ: 12.2.3 45. ANS: bowling DIF: L1 OBJ: 12.3.1 46. ANS: wall DIF: L2 OBJ: 12.3.1 47. ANS: equals DIF: L1 OBJ: 12.3.2
48. ANS: two DIF: L2 OBJ: 12.4.1 49. ANS: gravity DIF: L2 OBJ: 12.4.3 50. ANS: direction DIF: L2 OBJ: 12.4.4 SHORT ANSWER 51. ANS: The length of the arrow represents the size of the force, and the direction of the arrow represents the direction of the force. DIF: L2 OBJ: 12.1.1 52. ANS: It increases. DIF: L1 OBJ: 12.1.3 53. ANS: Each ball will reach the ground in the same amount of time. DIF: L2 OBJ: 12.1.5 54. ANS: Down; there is no net force on the sky diver. DIF: L1 OBJ: 12.2.2 55. ANS: Double the net force acting on the object. DIF: L1 OBJ: 12.2.2 56. ANS: The direction of the net force is opposite the direction of the dummy s motion. DIF: L2 OBJ: 12.2.2 57. ANS: equal in size, opposite in direction DIF: L1 OBJ: 12.3.1 58. ANS: The action force and the reaction force act on different objects. For forces to cancel, they must act on the same object. DIF: L1 OBJ: 12.3.1 59. ANS: law of conservation of momentum
DIF: L1 OBJ: 12.3.2 60. ANS: 20 kg m/s DIF: L2 OBJ: 12.3.2 61. ANS: The speed of the golf ball is much greater than the speed of the bowling ball. DIF: L2 OBJ: 12.3.2 62. ANS: attract and repel DIF: L1 OBJ: 12.4.1 63. ANS: The ends of the bar magnets will now repel each other. DIF: L1 OBJ: 12.4.1 64. ANS: strong nuclear force DIF: L1 OBJ: 12.4.2 65. ANS: the gravitational pull of the moon DIF: L1 OBJ: 12.4.3 PROBLEM 66. ANS: DIF: L2 OBJ: 12.2.2 67. ANS: DIF: L2 OBJ: 12.2.3 68. ANS:
DIF: L2 OBJ: 12.3.2 69. ANS: DIF: L2 OBJ: 12.2.2 ESSAY 70. ANS: On both the calm and windy days, the net force on the biker is zero because the biker is traveling at constant speed. On a calm day, the biker must pedal so that the forward-directed force applied to the bike balances the forces of friction opposing the forward motion. The friction forces primarily take the form rolling friction and fluid friction. On a windy day, the fluid friction force is much greater, so the rider must pedal harder to maintain the same constant speed. DIF: L2 OBJ: 12.1.2, 12.2.2 OTHER 71. ANS: D DIF: L1 OBJ: 12.4.4 72. ANS: The centripetal force will become less. DIF: L1 OBJ: 12.4.3 73. ANS: Earth DIF: L1 OBJ: 12.3.1 74. ANS: inertia DIF: L1 OBJ: 12.2.1 75. ANS: C DIF: L1 OBJ: 12.1.3 76. ANS: 0 kg m/s
DIF: L2 OBJ: 12.3.2 77. ANS: The momentums of both skaters are equal in size but opposite in direction. DIF: L2 OBJ: 12.3.2 78. ANS: The push on Skater B by Skater A accelerates Skater B forward. DIF: L2 OBJ: 12.2.1 79. ANS: According to Newton s third law of motion, as Skater A pushes on Skater B, an equal and opposite force pushes back on Skater A. The unbalanced force causes Skater B to accelerate backward. DIF: L2 OBJ: 12.1.2, 12.3.1 80. ANS: No; Skater A is exerting the same force on Skater B as before and so Skater B is exerting the same force on Skater A as before. The result is that Skater s A motion will be the same. DIF: L2 OBJ: 12.3.1