Queens College, CUNY - PHYSICS 152

Chapter 5—More Applications of Newton's Laws

MULTIPLE CHOICE

1)The total force needed to drag a box at constant speed across a surface with coefficient of kinetic friction ?_k is least when the force is applied at an angle ? such that

1. 1. sin? = ?_k.
   2. cos? = ?_k.
   3. tan? = ?_k.
   4. cot? = ?_k.
   5. sec? = ?_k.

2. A 4.0-kg block slides down a 35? incline at a constant speed when a 16-N force is applied acting up and parallel to the incline. What is the coefficient of kinetic friction between the block and the surface of the incline?

a.    0.20

b.   0.23

c.     0.26

d.   0.33

e.    0.41

3. A block is pushed across a horizontal surface by the force shown. If the coefficient of kinetic friction between the block and the surface is 0.30, F = 20 N, ? = 30?, and M = 3.0 kg, what is the magnitude of the acceleration of the block?

a.    2.8 m/s²

b.   2.3 m/s²

c.     1.8 m/s²

d.   3.3 m/s²

e.    5.4 m/s²

4. The block shown is pulled across the horizontal surface at a constant speed by the force shown. If M =

5.0 kg, F = 14 N and ? = 35?, what is the coefficient of kinetic friction between the block and the horizontal surface?

a.    0.44

b.   0.33

c.     0.38

d.   0.28

e.    0.17

5. In a game of shuffleboard (played on a horizontal surface), a puck is given an initial speed of 6.0 m/s. It slides a distance of 9.0 m before coming to rest. What is the coefficient of kinetic friction between the puck and the surface?

a.    0.20

b.   0.18

c.     0.15

d.   0.13

e.    0.27

6. A 2.0-kg block slides on a rough horizontal surface. A force (magnitude P = 4.0 N) acting parallel to the surface is applied to the block. The magnitude of the block's acceleration is 1.2 m/s². If P is increased to 5.0 N, determine the magnitude of the block's acceleration.

a.    2.1 m/s²

b.   2.3 m/s²

c.     1.9 m/s²

d.   1.7 m/s²

e.    3.2 m/s²

7. A 4.0-kg block is pushed up a 36? incline by a force of magnitude P applied parallel to the incline. When P is 31 N, it is observed that the block moves up the incline with a constant speed. What value of P would be required to lower the block down the incline at a constant speed?
   1. 27 N
   2. 15 N
   3. 13 N
   4. 17 N
   5. 19 N

8. A 1.8-kg block is released from rest at the top of a rough 30? inclined plane. As the block slides down the incline, its acceleration is 3.0 m/s² down the incline. Determine the magnitude of the force of friction acting on the block.
   1. 4.2 N
   2. 3.0 N
   3. 3.4 N

1. 4. 3.8 N
   5. 2.3 N

9. A 1.8-kg block is projected up a rough 10? inclined plane. As the block slides up the incline, its acceleration is 3.8 m/s² down the incline. What is the magnitude of the force of friction acting on the block?
   1. 5.0 N
   2. 3.8 N
   3. 4.2 N
   4. 4.6 N
   5. 6.5 N

10. A 2.0-kg block slides on a rough horizontal surface. A force (P = 6.0 N) is applied to the block as shown. The magnitude of the block's acceleration is 1.2 m/s². What is the magnitude of the force of friction acting on the block?

1. 1. 2.0 N
   2. 1.4 N
   3. 1.6 N
   4. 2.8 N
   5. 3.4 N

11. A 3.0-kg block slides on a rough horizontal surface. A force of 8.0 N acting parallel to the surface is applied to the block. The coefficient of kinetic friction between the block and the surface is 0.15. What is the magnitude of the block's acceleration?

a.    1.9 m/s²

b.   1.2 m/s²

c.     2.3 m/s²

d.   1.5 m/s²

e.    2.9 m/s²

12. A 1.0-kg block is pushed up a rough 22? inclined plane by a force of 7.0 N acting parallel to the incline. The acceleration of the block is 1.4 m/s² up the incline. Determine the magnitude of the force of friction acting on the block.
    1. 1.9 N
    2. 2.2 N
    3. 1.3 N
    4. 1.6 N
    5. 3.3 N

13. In the figure shown, the coefficient of kinetic friction between the block and the incline is 0.29. What is the magnitude of the acceleration of the suspended block as it falls? Disregard any pulley mass or friction in the pulley.

a.    5.4 m/s²

b.   5.2 m/s²

c.     4.9 m/s²

d.   5.6 m/s²

e.    7.9 m/s²

14. In the figure shown, the coefficient of kinetic friction between the block and the incline is 0.40. What is the magnitude of the acceleration of the suspended block as it falls? Disregard any pulley mass or friction in the pulley.

15. Two blocks in contact with each other are pushed to the right across a rough horizontal surface by the two forces shown. If the coefficient of kinetic friction between each of the blocks and the surface is 0.30, determine the magnitude of the force exerted on the 2.0-kg block by the 3.0-kg block.

1. 1. 15 N
   2. 25 N
   3. 11 N
   4. 22 N
   5. 33 N

16. Two blocks are accelerated across a horizontal frictionless surface as shown. Frictional forces keep the two blocks from sliding relative to each other, and the two move with the same acceleration. If F = 1.2 N and M = 1.0 kg, what is the horizontal component (frictional force) of the force of the large block on the small block?

1. 1. 0.40 N to the left
   2. 0.80 N to the right
   3. 0.40 N to the right
   4. 0.80 N to the left
   5. 1.20 N to the left

17. The coefficient of kinetic friction between the surface and the larger block is 0.25, and the coefficient of kinetic friction between the surface and the smaller block is 0.40. If F = 22N and M = 1.0 kg in the figure, what is the magnitude of the acceleration of either block?

a.    1.8 m/s²

b.   2.6 m/s²

c.     1.4 m/s²

d.   2.2 m/s²

e.    3.7 m/s²

18. In the figure, the coefficient of kinetic friction between the surface and the larger block is 0.20, and the coefficient of kinetic friction between the surface and the smaller block is 0.30. If F = 14 N and M =

1.0 kg, what is the magnitude of the acceleration of either block?

a.    2.0 m/s²

b.   1.3 m/s²

c.     1.5 m/s²

d.   1.8 m/s²

e.    3.5 m/s²

19. Two blocks are accelerated across a horizontal frictionless surface as shown. Frictional forces keep the two blocks from sliding relative to each other, and the two move with the same acceleration. If F = 1.2 N and M = 1.0 kg, what is the horizontal component (frictional force) of the force of the small block on the large block?

1. 1. 0.48 N to the right
   2. 0.72 N to the right
   3. 0.72 N to the left
   4. 0.48 N to the left
   5. 0.65 N to the left

20. Two blocks connected by a string are pulled across a horizontal surface by a force applied to one of the blocks, as shown. The coefficient of kinetic friction between the blocks and the surface is 0.25. If each block has an acceleration of 2.0 m/s² to the right, what is the magnitude F of the applied force?

1. 1. 25 N
   2. 18 N

21. In the figure, the coefficient of kinetic friction between the surface and the larger block is 0.20, and the coefficient of kinetic friction between the surface and the smaller block is 0.30. If F = 10 N and M =

1.0 kg, what is the tension in the connecting string?

22. The frictional force of the floor on a large suitcase is least when the suitcase is
    1. pushed by a force parallel to the floor.
    2. dragged by a force parallel to the floor.
    3. pulled by a force directed at an angle ? above the floor.
    4. pushed by a force directed at an angle ? into the floor.
    5. turned on its side and pushed by a force parallel to the floor.       
23. A 60-kg person rides down an icy hill of 20? slope while standing on a 3.0-kg flat-bottomed bathroom scale. Assume there is no frictional force between the bottom of the scale and the hill. The static friction force the scale exerts on the person is
    1. 0 N.

b.   201 N.

c.     211 N.

d.   553 N.

e.    580 N.

24. An object on the flat bed of a truck that is accelerating along a straight horizontal road. The coefficient of static friction is 0.300 in this case. Of the following choices, which is the lowest value of acceleration that would result in the object sliding on the bed of the truck?

a.    0.280 m/s²

b.   0.310 m/s²

c.     2.93 m/s²

d.   2.99 m/s²

e.    3.02 m/s²

25. The first of two identical boxes of mass m is sitting on level ground. The second box is sitting on a ramp that makes an angle with the ground. When a force of magnitude F is applied to each box in a direction parallel to the surface it is on, upwards on the box on the ramp, neither box moves. Which statement comparing the friction force on the box on the level, f_L, to the friction force on the box on the ramp, f_R, is correct?
    1. f_R = f_L
    2. f_R > f_L
    3. f_R < f_L
    4. The coefficient of static friction is needed to determine the correct answer.
    5. Depending on the values of the coefficient of static friction, the angle of elevation of the ramp, the mass of the boxes, and the applied force, answers (a), (b), and (c) are each a possible correct answer.

26. A race car travels 40 m/s around a banked (45? with the horizontal) circular (radius = 0.20 km) track. What is the magnitude of the resultant force on the 80-kg driver of this car?
    1. 0.68 kN
    2. 0.64 kN
    3. 0.72 kN
    4. 0.76 kN
    5. 0.52 kN

27. An airplane travels 80 m/s as it makes a horizontal circular turn which has a 0.80-km radius. What is the magnitude of the resultant force on the 75-kg pilot of this airplane?
    1. 0.69 kN
    2. 0.63 kN
    3. 0.66 kN
    4. 0.60 kN
    5. 0.57 kN

28. A car travels along the perimeter of a vertical circle (radius = 0.25 km) at a constant speed of 30 m/s. What is the magnitude of the resultant force on the 60-kg driver of the car at the lowest point on this circular path?
    1. 0.37 kN
    2. 0.80 kN
    3. 0.22 kN
    4. 0.59 kN
    5. 0.45 kN

29. A highway curve has a radius of 0.14 km and is unbanked. A car weighing 12 kN goes around the curve at a speed of 24 m/s without slipping. What is the magnitude of the horizontal force of the road on the car?
    1. 12 kN
    2. 17 kN
    3. 13 kN
    4. 5.0 kN
    5. 49 kN

30. A 4.0-kg mass on the end of a string rotates in a circular motion on a horizontal frictionless table. The mass has a constant speed of 2.0 m/s and the radius of the circle is 0.80 m. What is the magnitude of the resultant force acting on the mass?
    1. 39 N
    2. 20 N
    3. 44 N
    4. 0 N
    5. 30 N

31. A car travels around an unbanked highway curve (radius 0.15 km) at a constant speed of 25 m/s. What is the magnitude of the resultant force acting on the driver, who weighs 0.80 kN?
    1. 0.87 kN
    2. 0.34 kN
    3. 0.80 kN
    4. 0.00 kN
    5. 0.67 kN

32. A split highway has a number of lanes for traffic. For traffic going in one direction, the radius for the inside of the curve is half the radius for the outside. One car, car A, travels on the inside while another car of equal mass, car B, travels at equal speed on the outside of the curve. Which statement about resultant forces on the cars is correct?
    1. The force on A is half the force on B.
    2. The force on B is half the force on A.
    3. The force on A is four times the force on B.
    4. The force on B is four times the force on A.
    5. There is no net resultant force on either as long as they stay on the road while turning.       
33. A race car traveling at 100 m/s enters an unbanked turn of 400 m radius. The coefficient of (static) friction between the tires and the track is 1.1. The track has both an inner and an outer wall. Which statement is correct?
    1. The race car will crash into the outer wall.
    2. The race car will crash into the inner wall.
    3. The car will stay in the center of the track.
    4. The car will stay in the center of the track if the driver speeds up.
    5. The car would stay in the center of the track if the radius were reduced to 200 m.
34. A student is sitting on the right side of a school bus when it makes a right turn. We know that the force of gravity acts downwards and a normal force from the seat acts upwards. If the student stays in place when the bus turns, we also know that there must be
    1. no other force on the student.
    2. a force parallel to the seat directed forward on the student.
    3. a force parallel to the seat directed to the left on the student.
    4. a force parallel to the seat directed to the right on the student.
    5. a force parallel to the seat in a direction between forward and left on the student.

35. For a plane to be able to fly clockwise in a horizontal circle as seen from above, in addition to exerting a force downwards on the air
    1. it must be increasing its speed.
    2. it must exert a force on the air that is directed to the plane's left side.
    3. it must exert a force on the air that is directed to the plane's right side.
    4. it does not need to exert a force: it must only move the wing flaps out.
    5. it only needs to deflect the air without exerting any additional force on the air.       
36. When a car goes around a circular curve on a level road without slipping,
    1. no frictional force is needed because the car simply follows the road.
    2. the frictional force of the road on the car increases when the car's speed decreases.
    3. the frictional force of the road on the car increases when the car's speed increases.
    4. the frictional force of the road on the car increases when the car moves to the outside of the curve.
    5. there is no net frictional force because the road and the car exert equal and opposite forces on each other.

37. An iceboat is traveling in a circle on the ice. Halfway around the circle the sail and the steering mechanism fall off the boat. Which statement is correct?
    1. The boat will continue traveling in the circle because there is no friction.
    2. The boat will continue to travel in the circle because its velocity exerts a force on it.
    3. The boat will move off on a line tangent to the circle because there is no force on it.
    4. The boat will move off tangent to the circle because there is a force on it perpendicular to the boat directed to the outside of the circle.
    5. The boat will move off to the outside perpendicular to the tangent line since a force directed to the outside of the circle always acts on the boat.

38. A hornet circles around a pop can at constant speed once per second in a path with a 12-cm diameter.

We can conclude that the hornet's wings must push on the air with force components that are

1. 1. straight down.
   2. down and inwards.
   3. down and outwards.
   4. down and backwards.
   5. down, inwards and backwards.

39. A hornet circles around a pop can at increasing speed while flying in a path with a 12-cm diameter. We can conclude that the hornet's wings must push on the air with force components that are
    1. straight down.
    2. down and inwards.
    3. down and outwards.
    4. down and backwards.
    5. down, backwards and outwards.

40. Frank says that if you release the string when swinging a ball in a horizontal circle, the ball flies out in the radial direction defined by the string at the instant you release the ball. John says that it flies out along a tangent line perpendicular to the string, and that it then drops straight down to the ground. Which one, if either, is correct?
    1. Frank, because the centrifugal force is no longer counteracted by the string.
    2. Frank, because balls naturally fly straight out.
    3. John, because there is no centrifugal force.
    4. John, because balls fall straight down when released.
    5. Neither, because although there is no centrifugal force, and the ball's velocity is tangent to the circle at the instant of release, the ball then follows a parabolic trajectory.

41. 

    

    The coefficient of static friction for the tires of a race car is 0.950 and the coefficient of kinetic friction is 0.800. The car is on a level circular track of 50.0 m radius on a planet where                              compared

to Earth's                        . The maximum safe speed on the track on the planet is       times as large as the maximum safe speed on Earth.

a.    0.250

b.   0.500

c.     1.00

d.   2.00

e.    4.00

42. 

    

    The coefficient of static friction for the tires of a race car is 0.950 and the coefficient of kinetic friction is 0.800. The car is on a level circular track of 50.0 m radius on a planet where                              compared

to Earth's                        . If the car is to be able to travel at the same speed on the planet as on Earth, the radius of the track on the planet must be        times as large as the radius of the track on Earth.

a.    0.250

b.   0.500

c.     1.00

d.   2.00

e.    4.00

43. The following equation was obtained by solving a physics problem:

The best physical representation of the situation is

1. 1. A car traveling at 16.0 m/s is 19.2? into a turn of a quarter circle on a level road.
   2. A mass on a string that is originally horizontal has fallen to where the angle between the

string and the vertical direction is 19.2?.

1. 3. A mass on a string originally horizontal has fallen 19.2? from the horizontal direction.
   4. A car traveling at 16.0 m/s is on a circular curve banked at 19.2?.
   5. A car traveling at 16.0 m/s and going over a semicircular mountain-top road is 19.2? down from the top.

44. An airplane flies in a horizontal circle of radius 500 m at a speed of 150 m/s. If the plane were to fly in the same 500 m circle at a speed of 300 m/s, by what factor would its centripetal acceleration change? a.       0.25

b.   0.50

c.     1.00

d.   2.00

e.    4.00

45. An airplane flies in a horizontal circle of radius 500 m at a speed of 150 m/s. If the radius were changed to 1 000 m, but the speed remained the same, by what factor would its centripetal acceleration change?

a.    0.25

b.   0.50

c.     1.00

d.   2.00

e.    4.00

46. An airplane flies in a horizontal circle of radius 500 m at a speed of 150 m/s. If the plane were to fly in the same 1 000 m circle at a speed of 300 m/s, by what factor would its centripetal acceleration change?

a.    0.25

b.   0.50

c.     1.00

d.   2.00

e.    4.00

47. A car enters a level, unbanked semi-circular hairpin turn of 100 m radius at a speed of 28 m/s. The coefficient of friction between the tires and the road is ? = 0.800. If the car maintains a constant speed of 28 m/s, it will
    1. attempt to dig into the road surface.
    2. tend to veer toward the center of the semicircle.
    3. arrive safely at the end of the semicircle.
    4. tend to veer toward the outside of the circle.
    5. veer toward the center for the first quarter-circle, then veer toward the outside for the second quarter-circle.

48. A car enters a level, unbanked semi-circular hairpin turn of 300 m radius at a speed of 40 m/s. The coefficient of friction between the tires and the road is ? = 0.25. If the car maintains a constant speed of 40 m/s, it will

1. 1. attempt to dig into the road surface.
   2. tend to veer toward the center of the semicircle.
   3. arrive safely at the end of the semicircle.
   4. tend to veer toward the outside of the circle.
   5. veer toward the center for the first quarter-circle, then veer toward the outside for the second quarter-circle.

49. An airplane moves 140 m/s as it travels around a vertical circular loop which has a 1.0-km radius. What is the magnitude of the resultant force on the 70-kg pilot of this plane at the bottom of this loop?
    1. 2.1 kN
    2. 1.4 kN
    3. 0.69 kN
    4. 1.5 kN
    5. 1.3 kN

50. A 30-kg child rides on a circus Ferris wheel that takes her around a vertical circular path with a radius of 20 m every 22 s. What is the magnitude of the resultant force on the child at the highest point on this trajectory?
    1. 49 N
    2. 0.29 kN
    3. 0.34 kN
    4. 0.25 kN
    5. 0.76 kN

51. An amusement ride consists of a car moving in a vertical circle on the end of a rigid boom. The radius of the circle is 10 m. The combined weight of the car and riders is 5.0 kN. At the top of the circle the car has a speed of 5.0 m/s which is not changing at that instant. What is the force of the boom on the car at the top of the circle?
    1. 3.7 kN down
    2. 1.3 kN down
    3. 6.3 kN up
    4. 3.7 kN up
    5. 5.2 kN down

52. A stunt pilot weighing 0.70 kN performs a vertical circular dive of radius 0.80 km. At the bottom of the dive, the pilot has a speed of 0.20 km/s which at that instant is not changing. What force does the plane exert on the pilot?
    1. 3.6 kN up
    2. 4.3 kN up
    3. 2.9 kN down
    4. 2.9 kN up
    5. 5.8 kN down

53. A 0.50-kg mass attached to the end of a string swings in a vertical circle (radius = 2.0 m). When the mass is at the lowest point on the circle, the speed of the mass is 12 m/s. What is the magnitude of the force of the string on the mass at this position?
    1. 31 N
    2. 36 N
    3. 41 N
    4. 46 N
    5. 23 N

54. A roller-coaster car has a mass of 500 kg when fully loaded with passengers. The car passes over a hill of radius 15 m, as shown. At the top of the hill, the car has a speed of 8.0 m/s. What is the force of the track on the car at the top of the hill?

1. 1. 7.0 kN up
   2. 7.0 kN down
   3. 2.8 kN down
   4. 2.8 kN up
   5. 5.6 kN down

55. A 0.20-kg object attached to the end of a string swings in a vertical circle (radius = 80 cm). At the top of the circle the speed of the object is 4.5 m/s. What is the magnitude of the tension in the string at this position?
    1. 7.0 N
    2. 2.0 N
    3. 3.1 N
    4. 5.1 N
    5. 6.6 N

56. A roller-coaster car has a mass of 500 kg when fully loaded with passengers. At the bottom of a circular dip of radius 40 m (as shown in the figure) the car has a speed of 16 m/s. What is the magnitude of the force of the track on the car at the bottom of the dip?

1. 1. 3.2 kN
   2. 8.1 kN
   3. 4.9 kN
   4. 1.7 kN
   5. 5.3 kN

57. A 0.50 kg mass attached to the end of a string swings in a vertical circle (radius = 2.0 m). When the mass is at the highest point of the circle the speed of the mass is 8.0 m/s. What is the magnitude of the force of the string on the mass at this position?
    1. 21 N
    2. 11 N
    3. 16 N
    4. 26 N
    5. 36 N

58. A 50-kg child riding a Ferris wheel (radius = 10 m) travels in a vertical circle. The wheel completes one revolution every 10 s. What is the magnitude of the force on the child by the seat at the highest point on the circular path?
    1. 0.29 kN
    2. 0.49 kN
    3. 0.69 kN
    4. 0.20 kN
    5. 0.40 kN

59. A 0.30-kg mass attached to the end of a string swings in a vertical circle (R = 1.6 m), as shown. At an instant when ? = 50?, the tension in the string is 8.0 N. What is the magnitude of the resultant force on the mass at this instant?

1. 1. 5.6 N
   2. 6.0 N
   3. 6.5 N
   4. 5.1 N
   5. 2.2 N

60. An object attached to the end of a string swings in a vertical circle (R = 1.2 m), as shown. At an instant when ? = 30?, the speed of the object is 5.1 m/s and the tension in the string has a magnitude of 20 N. What is the mass of the object?

1. 1. 2.0 kg
   2. 1.5 kg
   3. 1.8 kg
   4. 1.2 kg
   5. 0.80 kg

61. A 0.40-kg mass attached to the end of a string swings in a vertical circle having a radius of 1.8 m. At an instant when the string makes an angle of 40 degrees below the horizontal, the speed of the mass is

5.0 m/s. What is the magnitude of the tension in the string at this instant?

1. 9.5 N
2. 3.0 N
3. 8.1 N
4. 5.6 N
5. 4.7 N

62. A 0.50-kg mass attached to the end of a string swings in a vertical circle (radius = 2.0 m). When the string is horizontal, the speed of the mass is 8.0 m/s. What is the magnitude of the force of the string on the mass at this position?
    1. 16 N
    2. 17 N
    3. 21 N
    4. 11 N
    5. 25 N

63. A 4.0-kg mass attached to the end of a string swings in a vertical circle of radius 2.0 m. When the string makes an angle of 35? with the vertical as shown, the speed of the mass is 5.0 m/s. At this instant what is the magnitude of the force the string exerts on the mass?

1. 1. 50 N
   2. 82 N
   3. 89 N
   4. 11 N
   5. 61 N

64. A rock attached to a string swings in a vertical circle. Which free body diagram could correctly describe the force(s) on the rock when it is at the highest point?

    1. 

       

       

       

       

       b.                                 c.                                  d.                                 e.

65. A rock attached to a string swings in a vertical circle. Which free body diagram could correctly describe the force(s) on the rock when the string is in one possible horizontal position?

    1. 

       

       

       c.                                                           e.

1. 2. 

      

      d.

66. A rock attached to a string swings in a vertical circle. Which free body diagram could correctly describe the force(s) on the rock when it is at the lowest point?

    1. 

       

       

       

       

       b.                                 c.                                  d.                                 e.

67. Two small cylindrical plastic containers with flat bottoms are placed on a turntable that has a smooth flat surface. Canister A is empty; canister B contains lead shot. Each canister is the same distance r from the center. The coefficient of static friction between the canisters and the turntable is ?_s. When the speed of the turntable is gradually increased,
    1. only the lighter container slides outward off the turntable; the heavier one stays on.
    2. only the heavier container slides outward off the turntable; the lighter one stays on.
    3. both containers slide off the turntable at the same turntable speed.
    4. the lighter container slides inward.
    5. the heavier container slides inward.

68. 

    The equation below is the solution to a problem.

.

The best physical representation of this equation is

68. 1. a sphere of 2.00 kg mass under a 6.00 N tension when at the bottom of a vertical circle.
    2. a sphere of 2.00 kg mass under a 6.00 N tension when at the side of a vertical circle.
    3. a sphere of 2.00 kg mass under a 6.00 N tension when at the top of a vertical circle.
    4. a sphere of 2.00 kg mass at any point on a horizontal circle.
    5. a 2.00 kg gecko running on the ceiling with a speed of 8.00 m/s.          
69. The equation below is the solution to a problem.

The best physical representation of this equation is

69. 1. a sphere of 2.00 kg mass under a 45.2 N tension when at the bottom of a vertical circle.
    2. a sphere of 2.00 kg mass under a 45.2 N tension when at the side of a vertical circle.
    3. a sphere of 2.00 kg mass under a 45.2 N tension when at the top of a vertical circle.
    4. a sphere of 2.00 kg mass at any point on a horizontal circle.
    5. a 2.00 kg gecko running on the ceiling with a speed of 8.00 m/s.

70. 

    The equation below is the solution to a problem.

.

The best physical representation of this equation is

70. 1. a sphere of 2.00 kg mass under a 25.6 N tension when at the bottom of a vertical circle.
    2. a sphere of 2.00 kg mass under a 25.6 N tension when at the side of a vertical circle.
    3. a sphere of 2.00 kg mass under a 25.6 N tension when at the top of a vertical circle.
    4. a sphere of 2.00 kg mass at any point on a horizontal circle.
    5. a 2.00 kg gecko running on the ceiling with a speed of 8.00 m/s.          
71. A skydiver of 75 kg mass has a terminal velocity of 60 m/s. At what speed is the resistive force on the skydiver half that when at terminal speed?
    1. 15 m/s
    2. 49 m/s
    3. 30 m/s
    4. 42 m/s
    5. 36 m/s

72. A boy on board a cruise ship drops a 30.0 gm marble into the ocean. If the resistive force proportionality constant is 0.500 kg/s, what is the terminal speed of the marble in m/s?

a.    0.147

b.   0.294

c.     0.588

d.   1.18

e.    2.35

73. If a 20-kg object dropped in air has a terminal speed of 60 m/s, what was its acceleration at 30 m/s? a. 9.80 m/s²

b.   7.35 m/s²

c.     4.90 m/s²

d. 2.45 m/s²

e.    More information is needed to answer this question.            

74. If a dense 20.0-kg object is falling in air at half its terminal velocity, what is the drag force on the object at this moment?

a.    24.5 N

b.   49.0 N

c.     69.3 N

d.   98.0 N

e.    139 N

75. What is the net force on a 10-kg solid steel sphere falling in air at terminal speed?
    1. 980 N
    2. 200 N
    3. 98 N
    4. 49 N
    5. Some value other than those given above.

PROBLEM

76. A box is dropped onto a conveyor belt moving at 2 m/s. If the coefficient of friction between the box and the belt is 0.3, how long before the box moves without slipping?

77. A sample of blood is placed into a centrifuge of radius 15.0 cm. The mass of a red corpuscle is 3.0 ? 10^?16 kg, and the centripetal force required to make it settle out of the plasma is 4.0 ? 10^?11 N. At how many revolutions per second should the centrifuge be operated?

78. A space station in the form of a large wheel, 120 m in diameter, rotates to provide an "artificial gravity" of 3.00 m/s² for persons located at the outer rim. Find the rotational frequency of the wheel (in revolutions per minute) that will produce this effect.

79. An airplane pilot experiences weightlessness as she passes over the top of a loop-the-loop maneuver. If her speed is 200 m/s at the time, find the radius of the loop.