CHAPTER 4 PHYSICS

12. A 3 000-kg sailboat experiences an eastward force of 4 500 N by the ocean tide and a wind force against its sails with magnitude of 5 800 N directed toward the northwest (45° N of W). What is the magnitude of the resultant acceleration? a. 1.4 m/s2 b. 3.2 m/s2 c. 2.4 m/s2 d. 3.4 m/s2 e. 1.3 m/s2

a

16. A 60.0-kg man jumps 1.70 m down onto a concrete walkway. His downward motion stops in 0.025 seconds. If he forgets to bend his knees, what force is transmitted to his leg bones? a. 13 900 N b. 346 N c. 8 000 N d. 1 790 N

a

2. If we know an object is moving at constant velocity, we may assume: a. the net force acting on the object is zero. b. there are no forces acting on the object. c. the object is accelerating. d. the object is losing mass.

a

21. A baseball batter hits an incoming 45.0-m/s fastball. The ball leaves the bat at 56.0 m/s after a ball-on-bat contact time of 0.040 s. What is the force exerted on the 0.25-kg baseball? a. 631 N b. 68.8 N c. 350 N d. 16.2 N e. 281 N

a

28. A horizontal force of 675 N is needed to overcome the force of static friction between a level floor and a 300-kg crate. What is the acceleration of the crate if the 675-N force is maintained after the crate begins to move and the coefficient of kinetic friction is 0.15? a. 0.78 m/s2 b. 3.7 m/s2 c. 3.3 m/s2 d. 1.5 m/s2 e. 1.8 m/s2

a

37. Dana uses a rope to pull a box that weighs 600 N across a level surface with constant velocity. The rope makes an angle of 40° above the horizontal and the tension in the rope is 400 N. What is the coefficient of friction? a. 0.89 b. 0.88 c. 2.00 d. 1.19 e. ​0.84

a

51. A 7.00-kg mass is placed on a 28.0° incline and friction keeps it from sliding. The coefficient of static friction in this case is 0.574, and the coefficient of sliding friction is 0.528. What is the frictional force in this situation? a. 32.2 N b. 60.6 N c. 32.0 N d. 34.8 N e. 3.29 N

a

53. Hector drives a pickup truck horizontally at 9.00 m/s. He is transporting a crate of delicate lead crystal. If the coefficient of static friction between the crate and the truck bed is 0.740, what is the minimum stopping distance for the truck so the crate will not slide? a. 5.58 m b. 6.66 m c. 81.0 m d. 15.6 m e. 2.79 m

a

6. An astronaut applies a force of 450 N to an asteroid, and it accelerates at 7.0 m/s2. What is the asteroid's mass? a. 64 kg b. 450 kg c. 460 kg d. 3 200 kg e. 0.016 kg

a

61. A box slides up an incline with an angle of elevation θ. When the box reaches its maximum distance up the incline it stops and does not slide down the incline due to friction. What is the minimum value of the coefficient of static friction for this to occur? a. μs = tanθ b. μs = sinθ c. μs = cosθ d. μs = 1

a

64. Two blocks of masses 20 kg and 9.0 kg are connected together by a light string and rest on a frictionless level surface. Attached to the 9.0-kg mass is another light string, which a person uses to pull both blocks horizontally. If the two-block system accelerates at 0.80 m/s2, what is the tension in the second string attached to the 9.0-kg mass? a. 23 N b. 14 N c. 16 N d. 7.2 N e. 25 N

a

68. As a 3.0-kg bucket is being lowered into a 14-m-deep well, starting from the top, the tension in the rope is 9.0 N. The acceleration of the bucket will be: a. 6.8 m/s2 downward. b. 9 m/s2 downward. c. zero. d. 3.0 m/s2 upward. e. 6.8 m/s2 upward.

a

7. Two ropes are attached to a 50-kg object. The first rope applies a force of 35 N and the second, 55 N. If the two ropes are perpendicular to each other, what is the resultant acceleration of the object? a. 1.3 m/s2 b. 35 m/s2 c. 1.8 m/s2 d. 65 m/s2 e. 0.77 m/s2

a

72. A sled weighs 160 N. It is held in place on a frictionless 25.0° slope by a rope attached to a stake at the top; the rope is parallel to the slope. What is the normal force of the slope acting on the sled? a. 145 N b. 67.6 N c. 177 N d. 379 N e. 74.6 N

a

73. A 650-N tightrope walker stands at the center of the rope such that each half of the rope makes an angle of 10.0° with the horizontal. What is the tension in the rope? a. 1 870 N b. 660 N c. 3 740 N d. 226 N e. 1 840 N

a

79. A trapeze artist, with swing, weighs 700 N; he is being held to one side by his partner so that the swing ropes make an angle of 40.0° with the vertical. In such a condition of static equilibrium, what is the tension in the rope? a. 9.1E+2 N b. 5.4E+2 N c. 700 N d. 1.4E+3 N e. 9.6E+2 N

a

83. An airplane of mass 1.7 × 104 kg tows a glider of mass 0.9 × 104 kg. The airplane propellers provide a net forward thrust of 4.0 × 104 N. What is the glider's acceleration? a. 1.5 m/s2 b. 2.4 m/s2 c. 5.0 m/s2 d. 4.4 m/s2 e. 9.8 m/s2

a

84. As a basketball player starts to jump for a rebound, he begins to move upward faster and faster until he leaves the floor. During this time that he is in contact with the floor, the force of the floor on his shoes is: a. bigger than his weight. b. equal in magnitude and opposite in direction to his weight. c. less than his weight. d. zero.

a

99. Three identical 4.0-kg cubes are placed on a horizontal frictionless surface in contact with one another. The cubes are lined up from left to right and a force is applied to the left side of the left cube causing all three cubes to accelerate to the right at 4.0 m/s2. What is the magnitude of the force exerted on the right cube by the middle cube in this case? a. 16 N b. 32 N c. 24 N d. 19 N e. none of the above

a

14. A cart of weight 15.0 N is accelerated across a level surface at 0.15 m/s2. What net force acts on the wagon? (g = 9.8 m/s2) a. 22 N b. 0.23 N c. 2.3 N d. 10 N e. 100 N

b

17. The accelerating force of the wind on a small 300-kg sailboat is 780 N northeast. If the drag of the keel is 552 N acting west, what is the acceleration of the boat? a. 4.4 m/s2 due east b. 1.8 m/s2 due north c. 2.6 m/s2 northeast d. 3.2 m/s2 north by northwest e. 0.23 m/s2 due east

b

19. An automobile of mass 2 500 kg moving at 50.0 m/s is braked suddenly with a constant braking force of 8 500 N. How far does the car travel before stopping? a. 7.35 m b. 368 m c. 184 m d. 551 m e. 19.2 m

b

20. A shot-putter moves his arm and the 6.00-kg shot through a distance of 1.25 m, giving the shot a velocity of 8.20 m/s from rest. Find the average force exerted on the shot during this time. a. 323 N b. 161 N c. 118 N d. 12.7 N e. 252 N

b

24. A thrown stone hits a window, but doesn't break it. Instead it reverses direction and ends up on the ground below the window. In this case, we know: a. the force of the stone on the glass > the force of the glass on the stone. b. the force of the stone on the glass = the force of the glass on the stone. c. the force of the stone on the glass < the force of the glass on the stone. d. the stone didn't slow down as it broke the glass.

b

30. A 150-kg crate is placed on an adjustable inclined plane. If the crate slides down the incline with an acceleration of 0.70 m/s2 when the incline angle is 20°, then what should the incline angle be for the crate to slide down the plane at constant speed? (g = 9.8 m/s2) a. 21° b. 16° c. 11° d. 26° e. ​6°

b

33. A 16-kg mass is placed on a 25° incline and friction keeps it from sliding. The coefficient of static friction in this case is 0.574 and the coefficient of sliding friction is 0.519. The mass is given a shove causing it to slide down the incline. Taking down the incline as positive, what is the acceleration of the mass while it is sliding? a. 0.47 m/s2 b. -0.47 m/s2 c. -0.96 m/s2 d. 0.96 m/s2 e. ​14.50 m/s2

b

35. A 300-N sled is pulled up a 28° slope at a constant speed by a force of 250 N. What is the coefficient of kinetic friction between sled and slope? a. 0.21 b. 0.41 c. 0.11 d. 1.55 e. ​2.95

b

38. A worker pulls a 350-N packing crate at constant velocity across a rough floor by exerting a force F = 200.0 N at an angle of 30.0° above the horizontal. What is the coefficient of kinetic friction of the floor? a. 0.793 b. 0.693 c. ​0.593 d. ​1.386 e. ​0.400

b

39. A hockey puck moving at 7.00 m/s coasts to a halt in 80.0 m on a smooth ice surface. What is the coefficient of friction between the ice and the puck? a. μ = 0.109 b. μ = 0.031 c. μ = 0.063 d. μ = 0.094 e. ​μ = 0.156

b

4. What condition must apply to a system's state of motion for it to be regarded as an inertial frame of reference? a. in decreasing velocity b. in constant velocity c. in constant acceleration d. in increasing acceleration

b

41. A block is launched up an incline plane. After going up the plane, it slides back down to its starting position. The coefficient of friction between the block and the plane is 0.3. The speed of the block when it reaches the starting position on the trip down: a. is the same as the launching speed. b. is less than the launching speed. c. is more than the launching speed. d. cannot be compared to the launch speed with the information given.

b

44. The figure shows a block on an inclined plane. What is the expression for the normal force acting on the block? a. Mg b. Mgcosθ c. Mgsinθ d. Mgtanθ

b

46. A 200-kg box is placed on a ramp. As one end of the ramp is raised, the box begins to move downward just as the angle of inclination reaches 18.0°. What is the coefficient of static friction between box and ramp? a. 0.42 b. 0.32 c. 3.1 d. 0.27 e. 62

b

49. There are nine books in a stack, each with a weight of 6 N. The coefficient of friction between all the books is 0.3 as is the coefficient between the table and the bottom book. What horizontal push must I just exceed on the next to bottom book to start sliding the top eight books off the bottom one? a. 1.80 N b. 14.4 N c. 48.0 N d. 16.2 N

b

50. Two objects, A and B, are placed on an inclined plane that can be rotated to different angles of elevation. A starts to slide at twice the angle of elevation that B starts sliding. The respective coefficients for static friction for A and B are μA and μB. Choose the last answer that is correct. a. μB > μA b. μA > μB c. μB = 2 μA d. μA = 2 μB

b

57. A box is to be moved across a level surface. A force of magnitude 200 N may be applied at an angle of 30° below the horizontal to push the box or at an angle of 30° above the horizontal to pull the box, either application sufficient to overcome friction and move the box. Which application will cause the box to have the greater acceleration? a. the one below the horizontal b. the one above the horizontal c. both give equal acceleration d. more information is needed

b

59. A sled is on a horizontal surface and a rope with tension T is pulling on it at an angle θ above the horizontal. The sled had mass M and does not move due to the frictional force. In this case the coefficient of friction is μ​s. In terms of the variables given and g, what is the magnitude of the frictional force in this case? a. μ​sMg b. Tcosθ c. Tsinθ d. μ​sMgcosθ

b

60. Which is the correct expression for the force of static friction, where n is the normal force? a. fs < ìsn b. fs ≤ ìsn c. fs > ìsn d. fs ≥ ìsn

b

69. A 5 500-N weight is held suspended in equilibrium by two cables. Cable 1 applies a horizontal force to the right of the object and has a tension, T1. Cable 2 applies a force upward and to the left at an angle of 40.0° to the negative x-axis and has a tension, T2. What is the tension, T1? a. 4.6E+3 N b. 6.6E+3 N c. 4.2E+3 N d. 8.6E+3 N e. 1.1E+4 N

b

74. A 500-N tightrope walker stands at the center of the rope. If the rope can withstand a tension of 1 800 N without breaking, what is the minimum angle the rope can make with the horizontal? a. 82° b. 8.0° c. 16° d. 0.40° e. 7.2°

b

77. Find the tension in an elevator cable if the 1 500-kg elevator is descending with an acceleration of 2.8 m/s2, downward. a. 1.9E+4 N b. 1.1E+4 N c. 4.2E+3 N d. 2.7E+1 N e. 2.1E+2 N

b

90. A man of weight W​man is standing on the second floor and is pulling on a rope to lift a box of weight W​box from the floor below. The rope, which is of negligible weight, has tension T in it, but the pull of the rope is insufficient to lift the box off the floor. What is the magnitude of the normal force that the second floor exerts on the man in this situation? a. W​man b. W​man + T c. W​man + T + a nonzero portion of W​box d. W​man + T + W​box

b

91. A cue ball of weight W is falling with an acceleration downward of g/3 and speed v. What is the magnitude of the drag force on the ball at this moment? a. W b. W c. W d. There is insufficient information to solve this problem.

b

96. A 16.0-kg mass and a 2.25-kg mass are connected by a light string over a massless, frictionless pulley. If g = 9.8 m/s2, what is the acceleration of the system when released? a. 13.0 m/s2 b. 7.38 m/s2 c. 179 m/s2 d. 9.80 m/s2 e. 1.86 m/s2

b

98. Three identical 6.0-kg cubes are placed on a horizontal frictionless surface in contact with one another. The cubes are lined up from left to right and a force is applied to the left side of the left cube causing all three cubes to accelerate to the right at 3.0 m/s2. What is the magnitude of the force exerted on the middle cube by the left cube in this case? a. 18 N b. 36 N c. 27 N d. 21 N e. none of the above

b

11. If we know that a nonzero net force is acting on an object, which of the following must we assume regarding the object's condition? The object is: a. at rest. b. moving with a constant velocity. c. being accelerated. d. losing mass.

c

15. Rita accelerates a 0.50-kg ball from rest to 8.0 m/s during the 0.14 s in which her foot is in contact with the ball. What average force does she apply to the ball during the kick? a. 110 N b. 22 N c. 29 N d. 56 N e. 2.2 N

c

18. A barefoot field-goal kicker imparts a speed of 30 m/s to a football at rest. If the football has a mass of 0.45 kg and time of contact with the football is 0.035 s, what is the force exerted on the foot? a. 14 N b. 13 N c. 390 N d. 860 N e. 900 N

c

22. In the terminology a 500-N block, the 500-N refers to the block's: a. mass. b. force. c. weight. d. None of the above.

c

23. The statement by Newton that "for every action there is an opposite but equal reaction" is regarded as which of his laws of motion? a. first b. second c. third d. fourth

c

26. A physics student is riding on a train traveling north. Having read about inertia, the student performs an experiment with a golf ball. He reaches over the aisle and drops the ball from rest. Instead of hitting the floor directly below the student's hand, it hits to the north, i.e., forward of that position. Which of the following might be the cause for this to happen? a. The train is moving at constant velocity. b. The train is speeding up. c. The train is slowing down. d. Whatever the cause, it cannot be any of the answers given.

c

27. A block of mass 4.0 kg rests on a horizontal surface where the coefficient of kinetic friction between the two is 0.20. A string attached to the block is pulled horizontally, resulting in a 3.0-m/s2 acceleration by the block. Find the tension in the string. (g = 9.80 m/s2) a. 12 N b. 7.8 N c. 20 N d. 4.2 N

c

29. A 150-kg crate is placed on an adjustable inclined plane. As one end of the incline is raised, the crate begins to move downward. If the crate slides down the plane with an acceleration of 0.20 m/s2 when the incline angle is 18°, what is the coefficient of kinetic friction between ramp and crate? (g = 9.8 m/s2) a. 0.40 b. 0.50 c. 0.30 d. 0.20 e. 2.8

c

3. Which of the following expresses a principle, which was initially stated by Galileo and was later incorporated into Newton's laws of motion? a. An object's acceleration is inversely proportional to its mass. b. For every action there is an equal but opposite reaction. c. The natural condition for a moving object is to remain in motion. d. The natural condition for a moving object is to come to rest.

c

31. Doug hits a hockey puck, giving it an initial velocity of 6.0 m/s. If the coefficient of kinetic friction between ice and puck is 0.20, how far will the puck slide before stopping? a. 14 m b. 19 m c. 9 m d. 11 m e. ​24 m

c

32. A 12.0-kg mass is placed on a 29.0° incline and friction keeps it from sliding. The coefficient of static friction in this case is 0.660, and the coefficient of sliding friction is 0.546. The mass is given a shove causing it to slide down the incline. What is the frictional force while the mass is sliding? a. 57.0 N b. 102.9 N c. 56.2 N d. 67.9 N e. ​10.5 N

c

34. A man pulls a sled at a constant velocity across a horizontal snow surface. If a force of 85 N is being applied to the sled rope at an angle of 56° to the ground, what is the force of friction between sled and snow? a. 85 N b. 70 N c. 48 N d. 5 N e. ​43 N

c

40. A block is launched up an incline plane. After going up the plane, it slides back down to its starting position. The coefficient of friction between the block and the plane is 0.3. The time for the trip up the plane: a. is the same as the time for the trip down. b. is more than the time for the trip down. c. is less than the time for the trip down. d. cannot be found without knowing the angle of inclination.

c

42. A crate of weight w is being pushed across a horizontal surface by a force directed at an angle of 20° below the horizontal. What is the magnitude of the normal force on the crate? a. It is less than w. b. It equals w. c. It is more than w. d. None of the above since the coefficient of kinetic friction is not given.

c

43. What forces are included in a free-body diagram for an object? a. The forces acting on the object and the forces the object exerts on any other objects it is in contact with. b. The forces acting on the object and the forces the object exerts on all other objects in the system. c. Only the forces acting on the object. d. Only forces internal to the object.

c

47. As a car goes up a hill, there is a force of friction between the road and the tires rolling on the road. The maximum force of friction is equal to: a. the weight of the car times the coefficient of kinetic friction. b. the normal force of the road times the coefficient of kinetic friction. c. the normal force of the road times the coefficient of static friction. d. zero.

c

54. The coefficient of static friction between the tires of a car and the street is μs = 0.70. Of the following, what is the steepest inclination angle of a street on which a car can be parked (with wheels locked) without slipping? a. 30° b. 40° c. 35° d. 45° e. ​32°

c

55. A 500-N block, on a 30.0° incline, is being held motionless by friction. The coefficient of static friction between the block and the plane is 0.63. The force due to friction is: a. 0 N. b. 433 N. c. 250 N. d. 500 N. e. 354 N.

c

58. A box of mass m is placed on an incline with angle of inclination θ. The box does not slide. The magnitude of the frictional force in this case is: a. μs mg sin θ. b. mg cos θ. c. mg sin θ. d. not given.

c

62. Two blocks, joined by a string, have masses of 3.0 and 4.0 kg. They rest on a frictionless horizontal surface. A second string, attached only to the 4.0-kg block, has horizontal force = 40 N applied to it. Both blocks accelerate. Find the tension in the string between the blocks. a. 23 N b. 5.7 N c. 17 N d. 93 N e. 120 N

c

63. Two blocks of masses 30.0 kg and 8.0 kg are connected together by a light string and rest on a frictionless level surface. Attached to the 8.0-kg mass is another light string, which a person uses to pull both blocks horizontally. If the two-block system accelerates at 0.60 m/s2 what is the tension in the connecting string between the blocks? a. 23 N b. 37 N c. 18 N d. 4.8 N e. 50 N

c

70. A 4 500-N weight is suspended in equilibrium by two cables. Cable 1 applies a horizontal force to the right of the object and has a tension, T1. Cable 2 applies a force upward and to the left at an angle of 37.0° to the negative x-axis and has a tension, T2. Find T2. a. 6.0E+3 N b. 2.7E+3 N c. 7.5E+3 N d. 5.6E+3 N e. 3.6E+3 N

c

75. A 20.0-kg traffic light hangs midway on a cable between two poles 30.0 meters apart. If the sag in the cable is 0.40 meters, what is the tension in each side of the cable? a. 9.8E+1 N b. 9.8E+3 N c. 3.7E+3 N d. 3.8E+2 N e. 2.0E+4 N

c

78. It is late and Carlos is sliding down a rope from his third-floor window to meet his friend Juan. As he slides down the rope faster and faster, he becomes frightened and grabs harder on the rope, increasing the tension in the rope. As soon as the upward tension in the rope becomes equal to his weight: a. Carlos will stop. b. Carlos will slow down. c. Carlos will continue down at a constant velocity. d. the rope must break.

c

8. Two forces act on a 8.50-kg object. One of the forces is 14.0 N. If the object accelerates at 3.50 m/s2, what is the greatest possible magnitude of the other force? a. 1.0 N b. 15.8 N c. 43.8 N d. 26.3 N e. 73.5 N

c

88. Jack pulls a sled across a level field by exerting a force of 120.0 N at an angle of 30.0° with the ground. What are the parallel and perpendicular components, respectively, of this force with respect to the ground? a. 208 N, 120 N b. 120 N, 208 N c. 104 N, 60 N d. 60 N, 104 N e. 69 N, 208 N

c

89. Five boys are pushing on a snowball, and each is pushing with a force of 10.0.0 N. However, each boy is pushing in a different direction. They are pushing north, northeast, east, southeast, and south. (Each boy is pushing at an angle of 45.0° relative to his neighbor.) What is the magnitude of the total force on the ball? a. 0 b. 14.1 N c. 24.1 N d. 11.4 N e. 48.3 N

c

93. A boxcar of mass 200 tons at rest becomes uncoupled on a 1.5° grade. If the track is considered to be frictionless, what speed does the boxcar have after 10 seconds? a. 0.37 m/s b. 0.59 m/s c. 2.6 m/s d. 4.3 m/s

c

95. The coefficient of friction between a racecar's wheels and the track is 1.0. The car starts from rest and accelerates at a constant rate for 275 m. Find the maximum speed at the end of the race. a. 52 m/s b. 57 m/s c. 73 m/s d. 86 m/s e. 66 m/s

c

1. Which of the following is an example of the type of force that acts at a distance? a. gravitational b. magnetic c. electrical d. all of the above

d

10. The acceleration due to gravity on the Moon's surface is one-sixth that on Earth. What net force would be required to accelerate a 25.0-kg object at 5.80 m/s2 on the Moon? a. 4.31 N b. 24.2 N c. 8.7 N d. 145 N e. 25.9 N

d

100. A 9.0-kg hanging weight is connected by a string over a pulley to a 5.0-kg block sliding on a flat table. If the coefficient of sliding friction is 0.19, find the tension in the string. ​ ​ a. 59.0 N b. 67.5 N c. 20.7 N d. 37.5 N

d

25. The net force on an object is in the positive x-direction. Consider the following statements. (I) The object can be moving in the negative x-direction. (II) The object can be speeding up. (III) The object can be slowing down. (IV) The object can be moving in the positive y-direction. Which of the statements are true? a. (I) and (II) b. (II) and (III) c. (III) and (IV) d. Choose this answer if all the statements are true.

d

36. Jamal pulls a 250-N sled up a 29.0° slope at constant speed by a force of 200 N. Near the top of the hill he releases the sled. With what acceleration does the sled go down the hill? a. 7.84 m/s2 b. 9.30 m/s2 c. 3.32 m/s2 d. 1.66 m/s2 e. ​2.66 m/s2

d

45. A horizontal force of 850 N is needed to overcome the force of static friction between a level floor and a 350-kg crate. If g = 9.8 m/s2, what is the coefficient of static friction? a. 24.8 b. 2.48 c. 4.04 d. 0.248 e. 2.43

d

48. As a car moves forward on a level road at constant velocity, the net force acting on the tires is: a. greater than the normal force times the coefficient of static friction. b. equal to the normal force times the coefficient of static friction. c. the normal force times the coefficient of kinetic friction. d. zero.

d

5. A 3.0-kg bowling ball experiences a net force of 8.0 N. What will be its acceleration? a. 24 m/s2 b. 3.0 m/s2 c. 8.0 m/s2 d. 2.7 m/s2 e. 0.38 m/s2

d

52. A 400-N crate rests on a ramp; the maximum angle just before it slips is 15.0° with the horizontal. What is the coefficient of static friction between crate and ramp surfaces? a. 3.7 b. 0.47 c. 2.1 d. 0.27 e. 0.40

d

56. The maximum possible value for the coefficient of static friction is: a. 0.50. b. 1.00. c. a value up to but not quite 1.00. d. greater than 1.00.

d

65. A 14-kg block rests on a level frictionless surface and is attached by a light string to a 5.0-kg hanging mass where the string passes over a massless frictionless pulley. If g = 9.8 m/s2, what is the tension in the connecting string? a. 2.6 N b. 21 N c. 49 N d. 36 N e. 190 N

d

66. An elevator weighing 20 000 N is supported by a steel cable. What is the tension in the cable when the elevator is being accelerated upward at a rate of 3.00 m/s2? (g = 9.80 m/s2) a. 6.1E+3 N b. 2.0E+4 N c. 6.0E+4 N d. 2.6E+4 N e. 6.7E+3 N

d

67. As I slide a box at constant speed up a frictionless slope, pulling parallel to the slope, the tension in the rope will be: a. greater than the tension would be if the box were stationary. b. greater than the weight of the box. c. equal to the weight of the box. d. less than the weight of the box.

d

71. A sled weighs 325 N. It is held in place on a frictionless 30.0° slope by a rope attached to a stake at the top; the rope is parallel to the slope. Find the tension in the rope. a. 281 N b. 650 N c. 375 N d. 163 N e. 188 N

d

76. A girl is using a rope to pull a box that weighs 300 N across a level surface with constant velocity. The rope makes an angle of 30° above the horizontal, and the tension in the rope is 100 N. What is the normal force of the floor on the box? a. 350 N b. 200 N c. 400 N d. 250 N e. 213 N

d

80. A string is attached to the ceiling. At the bottom of the string a rope of the same length as the string is attached. In the rope-string system, which of the following is the position of greatest tension? Assume the rope has more mass per unit length than the string. a. at the bottom of the rope b. at the top of the rope where it is attached to the string c. at the bottom of the string where it is attached to the rope d. at the top of the string

d

81. As I pull a rope connected to a box at constant speed up a frictionless slope, pulling parallel to the slope, the tension in the rope will be: a. greater than the tension would be if the box were stationary. b. greater than the weight of the box. c. equal to the weight of the box. d. less than the weight of the box.

d

85. A boxcar of mass 125 tons at rest becomes uncoupled on a 2.0° grade. If the track is considered to be frictionless, what speed does the boxcar have after 9.0 seconds? a. 4.0 m/s b. 0.038 m/s c. 31 m/s d. 3.1 m/s e. 0.31 m/s

d

86. A karate master strikes a board with an initial velocity of 12.0 m/s, decreasing to 3.0 m/s as his hand passes through the board. If the time of contact with the board is 0.002 s, and the mass of the coordinated hand and arm is 1.0 kg, what is the force exerted on the board? a. 7.5E+3 N b. 1.8E-2 N c. 3.0E-2 N d. 4.5E+3 N e. 6.0E+3 N

d

87. A trapeze artist, with swing, weighs 800 N; he is momentarily held to one side by his partner so that the swing ropes make an angle of 25.0° with the vertical. In such a condition of static equilibrium, what is the horizontal force being applied by the partner? a. 338 N b. 693 N c. 400 N d. 373 N e. 572 N

d

9. The acceleration due to gravity on the Moon's surface is one-sixth that on Earth. An astronaut's life support backpack weighs 250 lb on Earth. What does it weigh on the Moon? a. 1 500 lb b. 250 lb c. 256 lb d. 41.7 lb e. 244 lb

d

92. A baseball is moving in the air along the customary parabola. Ignoring air drag, where is the force on the baseball zero? a. at the top of the parabola b. just when it has started upward c. where it is about to impact d. nowhere

d

94. A 6.0-kg object is falling downward with an acceleration of 3.27 m/s2. Of the following values, which is nearest to the drag force on the object? a. 3.3 N b. 65 N c. 20 N d. 39 N

d

97. Two blocks are at rest on a horizontal frictionless surface with a compressed spring between them. The 15.0-kg block accelerates when the string holding the system in compression is cut and the 30.0-kg box accelerates in the opposite direction. What is the magnitude of the force from the expanding spring on the 30.0-kg box when the 15.0-kg box is undergoing an acceleration of 5.00 m/s2? a. 37.5 N b. 150 N c. 225 N d. 75.0 N e. 0 N

d

13. A 2 000-kg sailboat experiences an eastward force of 4 500 N by the ocean tide and a wind force against its sails with magnitude of 1 500 N directed toward the northwest (45° N of W). What is the direction of the resultant acceleration? a. 27° N of W b. 58° N of W c. 27° N of E d. 17° N of W e. 17° N of E

e

82. Three forces, 14.0 N, 25.0 N, and 20.0 N, are acting on a 9.6-kg object. Which of the following forces could also be acting on the object if it is moving with constant velocity? a. 1.0 N b. 17 N c. 30 N d. 5.0 N e. any of the above

e