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Problems

Combination conceptual/quantitative problem

Biological or medical application

Challenging problem

Detailed solution in the Student Solutions Manual

Problems paired by concept

Interactive or tutorial

4.1 Force

**1.**A person is standing on a bathroom scale. Which of the following is*not*a force exerted*on the scale:*a contact force due to the floor, a contact force due to the person's feet, the weight of the person, the weight of the scale?

2. A sack of flour has a weight of 19.8 N. What is its weight in pounds?

**3.**An astronaut weighs 175 lb. What is his weight in newtons?

4. Does the concept of a contact force apply to both a macroscopic scale and an atomic scale? Explain.

**5.**A force of 20 N is directed at an angle of 60° above the*x*-axis. A second force of 20 N is directed at an angle of 60° below the*x*-axis. What is the vector sum of these two forces?6. Juan is helping his mother rearrange the living room furniture. Juan pushes on the armchair with a force of 30 N directed at an angle of 15° above a horizontal line while his mother pushes with a force of 40 N directed at an angle of 20° below the same horizontal. What is the vector sum of these two forces?

7. In the drawing, what is the vector sum of forces if each grid square is 2 N on a side?

8. In the drawing, what is the vector sum of forces if each grid square is 2 N on a side?

**9.**Two of Robin Hood's men are pulling a sledge loaded with some gold along a path that runs due north to their hideout. One man pulls his rope with a force of 62 N at an angle of 12° east of north and the other pulls with the same force at an angle of 12° west of north. Assume the ropes are parallel to the ground. What is the sum of these two forces on the sledge?10. A barge is hauled along a straight-line section of canal by two horses harnessed to tow ropes and walking along the tow paths on either side of the canal. Each horse pulls with a force of 560 N at an angle of 15° with the centerline of the canal. Find the sum of the two forces exerted by the horses on the barge.

11. On her way to visit Grandmother, Red Riding Hood sat down to rest and placed her 1.2-kg basket of goodies beside her. A wolf came along, spotted the basket, and began to pull on the handle with a force of 6.4 N at an angle of 25° with respect to vertical. Red was not going to let go easily, so she pulled on the handle with a force of 12 N. If the net force on the basket is straight up, at what angle was Red Riding Hood pulling?

12. A parked automobile slips out of gear, rolls unattended down a slight incline, and then along a level road until it hits a stone wall. Draw an FBD to show the forces acting on the car while it is in contact with the wall.

**13.**Two objects,*A*and*B,*are acted on by the forces shown in the FBDs. Is the magnitude of the net force acting on object*B*greater than, less than, or equal to the magnitude of the net force acting on object*A?*Make a scale drawing on graph paper and explain the result.

14. Find the magnitude and direction of the net force on the object in each of the FBDs for this problem.

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**15.**A truck driving on a level highway is acted on by the following forces: a downward gravitational force of 52 kN (kilonewtons); an upward contact force due to the road of 52 kN; another contact force due to the road of 7 kN, directed east; and a drag force due to air resistance of 5 kN, directed west. What is the net force acting on the truck?

4.2 Inertia and Equilibrium: Newton's First Law of Motion; 4.3 Net Force, Mass, and Acceleration: Newton's Second Law of Motion

16. A sailboat, tied to a mooring with a line, weighs 820 N. The mooring line pulls horizontally toward the west on the sailboat with a force of 110 N. The sails are stowed away and the wind blows from the west. The boat is moored on a still lake—no water currents push on it. Draw an FBD for the sailboat and indicate the magnitude of each force.

**17.**A hummingbird is hovering motionless beside a flower. The blur of its wings shows that they are rapidly beating up and down. If the air pushes upward on the bird with a force of 0.30 N, what is the weight of the hummingbird?18. You are pulling a suitcase through the airport at a constant speed. The handle of the suitcase makes an angle of 60° with respect to the horizontal direction. If you pull with a force of 5.0 N parallel to the handle, what is the contact force due to the floor acting on the suitcase?

19. A model sailboat is slowly sailing west across a pond at 0.33 m/s. A gust of wind blowing at 28° south of west gives the sailboat a constant acceleration of magnitude 0.30 m/s

^{2}during a time interval of 2.0 s. (a) If the net force on the sailboat during the 2.0-s interval has magnitude 0.375 N, what is the sailboat's mass? (b) What is the new velocity of the boat after the 2.0-s gust of wind?20. A man is lazily floating on an air mattress in a swimming pool. If the weight of the man and air mattress together is 806 N, what is the upward force of the water acting on the mattress?

**21.**A bag of potatoes with weight 39.2 N is suspended from a string that exerts a force of 46.8 N. If the bag's acceleration is upward at 1.90 m/s^{2}, what is the mass of the potatoes?22. A 2010-kg elevator moves with an upward acceleration of 1.50 m/s

^{2}. What is the force exerted by the cable on the elevator?23. While an elevator of mass 2530 kg moves upward, the force exerted by the cable is 33.6 kN. (a) What is the acceleration of the elevator? (b) If at some point in the motion the velocity of the elevator is 1.20 m/s upward, what is the elevator's velocity 4.00 s later?

24. The vertical component of the acceleration of a sailplane is zero when the air pushes up against its wings with a force of 3.0 kN. (a) Assuming that the only forces on the sailplane are that due to gravity and that due to the air pushing against its wings, what is the gravitational force on the Earth due to the sailplane? (b) If the wing stalls and the upward force decreases to 2.0 kN, what is the acceleration of the sailplane?

**25.**A man lifts a 2.0-kg stone vertically with his hand at a constant upward velocity of 1.5 m/s. What is the magnitude of the total force of the man's hand on the stone?26. A man lifts a 2.0-kg stone vertically with his hand at a constant upward

*acceleration*of 1.5 m/s^{2}. What is the magnitude of the total force of the man's hand on the stone?27. What is the acceleration of an automobile of mass 1.40 × 10

^{3}kg when it is subjected to a forward force of 3.36 × 10^{3}N?28. A large wooden crate is pushed along a smooth, frictionless surface by a force of 100 N. The acceleration of the crate is measured to be 2.5 m/s

^{2}. What is the mass of the crate?**29.**The forces on a small airplane (mass 1160 kg) in horizontal flight heading eastward are as follows: gravity = 16.000 kN downward, lift = 16.000 kN upward, thrust = 1.800 kN eastward, and drag = 1.400 kN westward. At*t*= 0, the plane's speed is 60.0 m/s. If the forces remain constant, how far does the plane travel in the next 60.0 s?30. While an elevator of mass 832 kg moves downward, the tension in the supporting cable is a constant 7730 N. Between

*t*= 0 and*t*= 4.00 s, the elevator's displacement is 5.00 m downward. What is the elevator's speed at*t*= 4.00 s?

4.4 Interaction Pairs: Newton's Third Law of Motion

31. A hanging potted plant is suspended by a cord from a hook in the ceiling. Draw an FBD for each of these: (a) the system consisting of plant, soil, and pot; (b) the cord; (c) the hook; (d) the system consisting of plant, soil, pot, cord, and hook. Label each force arrow using subscripts (for example, would represent the force exerted on the cord by the hook).

32. A bike is hanging from a hook in a garage. Consider the following forces: (a) the force of the Earth pulling down on the bike, (b) the force of the bike pulling up on the Earth, (c) the force of the hook pulling up on the bike, and (d) the force of the hook pulling down on the ceiling. Which two forces are equal and opposite because of Newton's third law? Which two forces are equal and opposite because of Newton's first law?

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**33.**A woman who weighs 600 N sits on a chair with her feet on the floor and her arms resting on the chair's armrests. The chair weighs 100 N. Each armrest exerts an upward force of 25 N on her arms. The seat of the chair exerts an upward force of 500 N. (a) What force does the floor exert on her feet? (b) What force does the floor exert on the chair? (c) Consider the woman and the chair to be a single system. Draw an FBD for this system that includes all of the*external*forces acting on it.

34. A fisherman is holding a fishing rod with a large fish suspended from the line of the rod. Identify the forces acting on the rod and their interaction partners.

**35.**A fish is suspended by a line from a fishing rod. Choose two forces acting on the fish and describe the interaction partner of each.

36. A skydiver, who weighs 650 N, is falling at a constant speed with his parachute open. Consider the apparatus that connects the parachute to the skydiver to be part of the parachute. The parachute pulls upward with a force of 620 N. (a) What is the force of the air resistance acting on the skydiver? (b) Identify the forces and the interaction partners of each force exerted on the skydiver. (c) Identify the forces and interaction partners of each force exerted on the parachute.

**37.**Margie, who weighs 543 N, is standing on a bathroom scale that weighs 45 N. (a) With what force does the scale push up on Margie? (b) What is the interaction partner of that force? (c) With what force does the Earth push up on the scale? (d) Identify the interaction partner of that force.38. Refer to Problem 36. Consider the skydiver and parachute to be a single system. What are the external forces acting on this system?

4.5 Gravitational Forces

39. (a) Calculate your weight in newtons. (b) What is the weight in newtons of 250 g of cheese? (c) Name a common object whose weight is about 1 N.

40. A young South African girl has a mass of 40.0 kg. (a) What is her weight in newtons? (b) If she came to the United States, what would her weight be in pounds as measured on an American scale? Assume

*g*= 9.80 N/kg in both locations.**41.**A man weighs 0.80 kN on Earth. What is his mass in kilograms?

42. An astronaut stands at a position on the Moon such that Earth is directly over head and releases a Moon rock that was in her hand. (a) Which way will it fall? (b) What is the gravitational force exerted by the Moon on a 1.0-kg rock resting on the Moon's surface? (c) What is the gravitational force exerted by the Earth on the same 1.0-kg rock resting on the surface of the Moon? (d) What is the net gravitational force on the rock?

43. Alex is on stage playing his bass guitar. Estimate the magnitude of the

*gravitational*attraction between Alex and Pat, a fan who is standing 8 m from Alex. Alex has a mass of 55 kg and Pat has a mass of 40 kg.44. The Space Shuttle carries a satellite in its cargo bay and places it into orbit around the Earth. Find the ratio of the Earth's gravitational force on the satellite when it is on a launch pad at the Kennedy Space Center to the gravitational force exerted when the satellite is orbiting 6.00 × 10

^{3}km above the launch pad.**45.**How far above the surface of the Earth does an object have to be in order for it to have the same weight as it would have on the surface of the Moon? (Ignore any effects from the Earth's gravity for the object on the Moon's surface or from the Moon's gravity for the object above the Earth.)46. Find and compare the weight of a 65-kg man on Earth with the weight of the same man on (a) Mars, where

*g*= 3.7 N/kg; (b) Venus, where*g*= 8.9 N/kg; and (c) Earth's Moon, where*g*= 1.6 N/kg.47. Find the altitudes above the Earth's surface where Earth's gravitational field strength would be (a) two thirds and (b) one third of its value at the surface. [

*Hint:*First find the radius for each situation; then recall that the altitude is the distance from the*surface*to a point above the surface. Use proportional reasoning.]48. During a balloon ascension, wearing an oxygen mask, you measure the weight of a calibrated 5.00-kg mass and find that the value of the gravitational field strength at your location is 9.792 N/kg. How high above sea level, where the gravitational field strength was measured to be 9.803 N/kg, are you located?

**49.**At what altitude above the Earth's surface would your weight be half of what it is at the Earth's surface?50. (a) What is the magnitude of the gravitational force that the Earth exerts on the Moon? (b) What is the magnitude of the gravitational force that the Moon exerts on the Earth? See the inside front and back covers for necessary information.

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51. What is the approximate magnitude of the gravitational force between the Earth and the Voyager spacecraft when they are separated by 15 billion km? Each spacecraft has a mass of approximately 825 kg during the mission, although the mass at launch was 2100 kg because of expendable Titan-Centaur rockets.

52. In free fall, we assume the acceleration to be constant. Not only is air resistance ignored, but the gravitational field strength is assumed to be constant. From what height can an object fall to the Earth's surface such that the gravitational field strength changes less than 1.000% during the fall?

4.6 Contact Forces

**53.**A book rests on the surface of the table. Consider the following four forces that arise in this situation: (a) the force of the Earth pulling on the book, (b) the force of the table pushing on the book, (c) the force of the book pushing on the table, and (d) the force of the book pulling on the Earth. The book is not moving. Which pair of forces must be equal in magnitude and opposite in direction even though they are*not*an interaction pair?54. A crate full of artichokes rests on a ramp that is inclined 10.0° above the horizontal. Give the direction of the normal force and the friction force acting on the crate in each of these situations. (a) The crate is at rest. (b) The crate is being pushed and is sliding up the ramp. (c) The crate is being pushed and is sliding down the ramp.

55. Mechanical advantage is the ratio of the force required without the use of a simple machine to that needed when using the simple machine. Compare the force to lift an object with that needed to slide the same object up a frictionless incline and show that the mechanical advantage of the inclined plane is the length of the incline divided by the height of the incline (

*d/h*in Fig. 4.25).56. An 80.0-N crate of apples sits at rest on a ramp that runs from the ground to the bed of a truck. The ramp is inclined at 20.0° to the ground. (a) What is the normal force exerted on the crate by the ramp? (b) The interaction partner of this normal force has what magnitude and direction? It is exerted

*by*what object*on*what object? Is it a contact or a long-range force? (c) What is the static frictional force exerted on the crate by the ramp? (d) What is the minimum possible value of the coefficient of static friction? (e) The normal and frictional forces are perpendicular components of the contact force exerted on the crate by the ramp. Find the magnitude and direction of the contact force.**57.**An 85-kg skier is sliding down a ski slope at a constant velocity. The slope makes an angle of 11° above the horizontal direction. (a) Ignoring any air resistance, what is the force of kinetic friction acting on the skier? (b) What is the coefficient of kinetic friction between the skis and the snow?Problems 58–60. A crate of potatoes of mass 18.0 kg is on a ramp with angle of incline 30° to the horizontal. The coefficients of friction are μ

_{s}= 0.75 and μ_{k}= 0.40. Find the frictional force (magnitude and direction) on the crate if

58. the crate is at rest.

**59.**the crate is sliding down the ramp.60. the crate is sliding

*up*the ramp.

**61.**You grab a book and give it a quick push across the top of a horizontal table. After a short push, the book slides across the table, and because of friction, comes to a stop. (a) Draw an FBD of the book while you are pushing it. (b) Draw an FBD of the book after you have stopped pushing it, while it is sliding across the table. (c) Draw an FBD of the book after it has stopped sliding. (d) In which of the preceding cases is the net force on the book not equal to zero? (e) If the book has a mass of 0.50 kg and the coefficient of friction between the book and the table is 0.40, what is the net force acting on the book in part (b)? (f) If there were no friction between the table and the book, what would the free-body diagram for part (b) look like? Would the book slow down in this case? Why or why not?62. (a) In Example 4.10, if the movers stop pushing on the safe, can static friction hold the safe in place without having it slide back down? (b) If not, what minimum force needs to be applied to hold the safe in place?

**63.**A 3.0-kg block is at rest on a horizontal floor. If you push horizontally on the 3.0-kg block with a force of 12.0 N, it just starts to move. (a) What is the coefficient of static friction? (b) A 7.0-kg block is stacked on top of the 3.0-kg block. What is the magnitude*F*of the force, acting horizontally on the 3.0-kg block as before, that is required to make the two blocks start to move?64. A horse is trotting along pulling a sleigh through the snow. To move the sleigh, of mass

*m,*straight ahead at a constant speed, the horse must pull with a force of magnitude*T.*(a) What is the net force acting on the sleigh? (b) What is the coefficient of kinetic friction between the sleigh and the snow?

**65.**Before hanging new William Morris wallpaper in her bedroom, Brenda sanded the walls lightly to smooth out some irregularities on the surface. The sanding block weighs 2.0 N and Brenda pushes on it with a force of 3.0 N at an angle of 30.0° with respect to the vertical, and angled toward the wall. Draw an FBD for the sanding block as it moves straight up the wall at a constant speed. What is the coefficient of kinetic friction between the wall and the block?- Page 136
66. Four separate blocks are placed side by side in a left-to-right row on a table. A horizontal force, acting toward the right, is applied to the block on the far left end of the row. Draw FBDs for (a) the second block on the left and for (b) the system of four blocks.

67. A box sits on a horizontal wooden ramp. The coefficient of static friction between the box and the ramp is 0.30. You grab one end of the ramp and lift it up, keeping the other end of the ramp on the ground. What is the angle between the ramp and the horizontal direction when the box begins to slide down the ramp?

Tutorial: Crate on a Ramp

68. In a playground, two slides have different angles of incline θ

_{1}and θ_{2}(θ_{2}> θ_{1}). A child slides down the first at constant speed; on the second, his acceleration down the slide is*a.*Assume the coefficient of kinetic friction is the same for both slides. (a) Find*a*in terms of θ_{1}, θ_{2}, and*g.*(b) Find the numerical value of*a*for θ_{1}= 45° and θ_{2}= 61°.

4.7 Tension

**69.**A sailboat is tied to a mooring with a horizontal line. The wind is from the southwest. Draw an FBD and identify all the forces acting on the sailboat.70. A towline is attached between a car and a glider. As the car speeds due east along the runway, the towline exerts a horizontal force of 850 N on the glider. What is the magnitude and direction of the force exerted by the glider on the towline?

71. In Example 4.14, find the tension in the coupling between cars 2 and 3.

Tutorial: Towing a Train

72. A 200.0-N sign is suspended from a horizontal strut of negligible weight. The force exerted on the strut by the wall is horizontal. Draw an FBD to show the forces acting on the strut. Find the tension

*T*in the diagonal cable supporting the strut.**73.**Two boxes with different masses are tied together on a frictionless ramp surface. What is the tension in each of the cords?

74. A pulley is attached to the ceiling. Spring scale A is attached to the wall and a rope runs horizontally from it and over the pulley. The same rope is then attached to spring scale B. On the other side of scale B hangs a 120-N weight. What are the readings of the two scales A and B? The weights of the scales are negligible.

**75.**Spring scale A is attached to the floor and a rope runs vertically upward, loops over the pulley, and runs down on the other side to a 120-N weight. Scale B is attached to the ceiling and the pulley is hung below it. What are the readings of the two spring scales, A and B? Neglect the weights of the pulley and scales.

76. Two springs are connected in series so that spring scale A hangs from a hook on the ceiling and a second spring scale, B, hangs from the hook at the bottom of scale A. Apples weighing 120 N hang from the hook at the bottom of scale B. What are the readings on the upper scale A and the lower scale B? Ignore the weights of the scales.

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**77.**A pulley is hung from the ceiling by a rope. A block of mass*M*is suspended by another rope that passes over the pulley and is attached to the wall. The rope fastened to the wall makes a right angle with the wall. Ignore the masses of the rope and the pulley. Find (a) the tension in the rope from which the pulley hangs and (b) the angle θ that the rope makes with the ceiling. 78. A 2.0-kg ball tied to a string fixed to the ceiling is pulled to one side by a force Just before the ball is released and allowed to swing back and forth, (a) how large is the force that is holding the ball in position and (b) what is the tension in the string?

79. A 45-N lithograph is supported by two wires. One wire makes a 25° angle with the vertical and the other makes a 15° angle with the vertical. Find the tension in each wire.

Tutorial: Hanging Picture

80. A crow perches on a clothesline midway between two poles. Each end of the rope makes an angle of θ below the horizontal where it connects to the pole. If the weight of the crow is

*W,*what is the tension in the rope? Ignore the weight of the rope.**81.**The drawing shows an elastic cord attached to two back teeth and stretched across a front tooth. The purpose of this arrangement is to apply a force to the front tooth. (The figure has been simplified by running the cord straight from the front tooth to the back teeth.) If the tension in the cord is 1.2 N, what are the magnitude and direction of the force applied to the front tooth?82. A cord, with a spring balance to measure forces attached midway along, is hanging from a hook attached to the ceiling. A mass of 10 kg is hanging from the lower end of the cord. The spring balance indicates a reading of 98 N for the force. Then two people hold the opposite ends of the same cord and pull against each other horizontally until the balance in the middle again reads 98 N. With what force must each person pull to attain this result?

83. Two blocks, masses

*m*_{1}and*m*_{2}, are connected by a massless cord. If the two blocks are pulled with a constant tension on a frictionless surface by applying a force of magnitude*T*_{2}to a second cord connected to*m*_{2}, what is the ratio of the tensions in the two cords*T*_{1}/*T*_{2}in terms of the masses?

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4.8 Applying Newton's Second Law

84. A 6.0-kg block, starting from rest, slides down a frictionless incline of length 2.0 m. When it arrives at the bottom of the incline, its speed is

*v*_{f}. At what distance from the top of the incline is the speed of the block 0.50*v*_{f}?**85.**The coefficient of static friction between a block and a horizontal floor is 0.40, while the coefficient of kinetic friction is 0.15. The mass of the block is 5.0 kg. A horizontal force is applied to the block and slowly increased. (a) What is the value of the applied horizontal force at the instant that the block starts to slide? (b) What is the net force on the block after it starts to slide?86. A 2.0-kg toy locomotive is pulling a 1.0-kg caboose. The frictional force of the track on the caboose is 0.50 N backward along the track. If the train's acceleration forward is 3.0 m/s

^{2}, what is the magnitude of the force exerted by the locomotive on the caboose?87. A block of mass

*m*_{1}= 3.0 kg rests on a frictionless horizontal surface. A second block of mass*m*_{2}= 2.0 kg hangs from an ideal cord of negligible mass that runs over an ideal pulley and then is connected to the first block. The blocks are released from rest. (a) Find the acceleration of the two blocks after they are released. (b) What is the velocity of the first block 1.2 s after the release of the blocks, assuming the first block does not run out of room on the table and the second block does not land on the floor? (c) How far has block 1 moved during the 1.2-s interval? (d) What is the displacement of the blocks from their initial positions 0.40 s after they are released?88. An engine pulls a train of 20 freight cars, each having a mass of 5.0 × 10

^{4}kg with a constant force. The cars move from rest to a speed of 4.0 m/s in 20.0 s on a straight track. Ignoring friction, what is the force with which the 10th car pulls the 11th one (at the middle of the train)?Tutorial: School Bus

**89.**In Fig. 4.44, two blocks are connected by a lightweight, flexible cord that passes over a frictionless pulley. (a) If*m*_{1}= 3.0 kg and*m*_{2}= 5.0 kg, what are the accelerations of each block? (b) What is the tension in the cord?90. A rope is attached from a truck to a 1400-kg car. The rope will break if the tension is greater than 2500 N. Ignoring friction, what is the maximum possible acceleration of the truck if the rope does not break? Should the driver of the truck be concerned that the rope might break?

91. Two blocks are connected by a lightweight, flexible cord that passes over a frictionless pulley. If

*m*_{1}= 3.6 kg and*m*_{2}= 9.2 kg, and block 2 is initially at rest 140 cm above the floor, how long does it take block 2 to reach the floor?92. A 10.0-kg watermelon and a 7.00-kg pumpkin are attached to each other via a cord that wraps over a pulley, as shown. Friction is negligible everywhere in this system. (a) Find the accelerations of the pumpkin and the watermelon. Specify magnitude and direction. (b) If the system is released from rest, how far along the incline will the pumpkin travel in 0.30 s? (c) What is the speed of the watermelon after 0.20 s?

Tutorial: Pulley

Tutorial: Pulley

**93.**In the physics laboratory, a glider is released from rest on a frictionless air track inclined at an angle. If the glider has gained a speed of 25.0 cm/s in traveling 50.0 cm from the starting point, what was the angle of inclination of the track? Draw a graph of*v*_{x}(*t*) when the positive*x*-axis points down the track.94. A 10.0-kg block is released from rest on a frictionless track inclined at an angle of 55°. (a) What is the net force on the block after it is released? (b) What is the acceleration of the block? (c) If the block is released from rest, how long will it take for the block to attain a speed of 10.0 m/s? (d) Draw a motion diagram for the block. (e) Draw a graph of

*v*_{x}(*t*) for values of velocity between 0 and 10 m/s. Let the positive*x*-axis point down the track.

95. A box full of books rests on a wooden floor. The normal force the floor exerts on the box is 250 N. (a) You push horizontally on the box with a force of 120 N, but it refuses to budge. What can you say about the coefficient of static friction between the box and the floor? (b) If you must push horizontally on the box with a force of at least 150 N to start it sliding, what is the coefficient of static friction? (c) Once the box is sliding, you only have to push with a force of 120 N to keep it sliding. What is the coefficient of kinetic friction?

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96. A helicopter is lifting two crates simultaneously. One crate with a mass of 200 kg is attached to the helicopter by a cable. The second crate with a mass of 100 kg is hanging below the first crate and attached to the first crate by a cable. As the helicopter accelerates upward at a rate of 1.0 m/s

^{2}, what is the tension in each of the two cables?

4.10 Apparent Weight

**97.**Oliver has a mass of 76.2 kg. He is riding in an elevator that has a downward acceleration of 1.37 m/s^{2}. With what magnitude force does the elevator floor push upward on Oliver?98. While on an elevator, Jaden's apparent weight is 550 N. When he is on the ground, the scale reading is 600 N. What is Jaden's acceleration?

99. When on the ground, Ian's weight is measured to be 640 N. When Ian is on an elevator, his apparent weight is 700 N. What is the net force on the system (Ian and the elevator) if their combined mass is 1050 kg?

100. Refer to Example 4.19. What is the apparent weight of the same passenger (weighing 598 N) in the following situations? In each case, the magnitude of the elevator's acceleration is 0.50 m/s

^{2}. (a) After having stopped at the 15th floor, the passenger pushes the 8th floor button; the elevator is beginning to move downward. (b) The elevator is moving downward and is slowing down as it nears the 8th floor.**101.**You are standing on a bathroom scale inside an elevator. Your weight is 140 lb, but the reading of the scale is 120 lb. (a) What is the magnitude and direction of the acceleration of the elevator? (b) Can you tell whether the elevator is speeding up or slowing down?

102. Yolanda, whose mass is 64.2 kg, is riding in an elevator that has an upward acceleration of 2.13 m/s

^{2}. What force does she exert on the floor of the elevator?

**103.**Felipe is going for a physical before joining the swim team. He is concerned about his weight, so he carries his scale into the elevator to check his weight while heading to the doctor's office on the 21st floor of the building. If his scale reads 750 N while the elevator has an upward acceleration of 2.0 m/s^{2}, what does the nurse measure his weight to be?104. Luke stands on a scale in an elevator that has a constant acceleration upward. The scale reads 0.960 kN. When Luke picks up a box of mass 20.0 kg, the scale reads 1.200 kN. (The acceleration remains the same.) (a) Find the acceleration of the elevator. (b) Find Luke's weight.

4.12 Fundamental Forces

**105.**Which of the fundamental forces has the shortest range, yet is responsible for producing the sunlight that reaches Earth?106. Which of the fundamental forces governs the motion of planets in the solar system? Is this the strongest or the weakest of the fundamental forces? Explain.

107. Which of the following forces have an unlimited range: strong force, contact force, electromagnetic force, gravitational force?

108. Which of the following forces bind electrons to nuclei to form atoms: strong force, contact force, electromagnetic force, gravitational force?

**109.**Which of the fundamental forces binds quarks together to form protons, neutrons, and many exotic subatomic particles?