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Physics 1401 - Exam 2

Chapter 5N-New

2. The second hand on a watch has a length of 4.50 mm and makes one revolution in

60.00 s. What is the speed of the end of the second hand as it moves in uniform circular

motion?

(a) 9.42 × 10-4 m/s (c) 5.34 × 10-

3 m/s (e) 2.36 × 10-

5 m/s

(b) 2.67 × 10-3 m/s (d) 4.71 × 10-

4 m/s

3. Approximately one billion years ago, the Moon orbited the Earth much closer than it

does today. The radius of the orbit was only 24 400 km. Today, the radius is 385 000 km.

The orbital period was only 23 400 s. The present period is 2.36 × 106 s. Assume that the

orbit of the Moon is circular. Calculate the ratio of the speed of the Moon in its ancient

orbit to the speed that it has today.

(a) 15.8 (c) 10.2 (e) 6.39

(b) 12.8 (d) 7.15

5. A ball is whirled on the end of a string in a horizontal circle of radius R at constant

speed v. The centripetal acceleration of the ball can be increased by a factor of 4 by

(a) keeping the speed fixed and increasing the radius by a factor of 4.

(b) keeping the radius fixed and increasing the speed by a factor of 4.

(c) keeping the radius fixed and increasing the period by a factor of 4.

(d) keeping the radius fixed and decreasing the period by a factor of 4.

(e) keeping the speed fixed and decreasing the radius by a factor of 4.

7. A car traveling at 20 m/s rounds a curve so that its centripetal acceleration is 5 m/s2.

What is the radius of the curve?

(a) 4 m (c) 80 m (e) 640 m

(b) 8 m (d) 160 m


8. A satellite is placed in a circular orbit to observe the surface of Mars from an altitude

of 144 km. The equatorial radius of Mars is 3397 km. If the speed of the satellite is 3480

m/s, what is the magnitude of the centripetal acceleration of the satellite?

(a) 2.17 m/s2 (c) 2.99 m/s

2 (e) 4.05 m/s

2

(b) 2.60 m/s2 (d) 3.42 m/s

2

11. A boy is whirling a stone around his head by means of a string. The string makes one

complete revolution every second, and the tension in the string is FT. The boy then

speeds up the stone, keeping the radius of the circle unchanged, so that the string makes

two complete revolutions every second. What happens to the tension in the sting?

(a) The tension is unchanged.

(b) The tension reduces to half of its original value.

(c) The tension increases to twice its original value.

(d) The tension increases to four times its original value.

(e) The tension reduces to one-fourth of its original value.

14. Sara puts a box into the trunk of her car. Later, she drives around an unbanked curve

that has a radius of 48 m. The speed of the car on the curve is 16 m/s, but the box remains

stationary relative to the floor of the trunk. Determine the minimum coefficient of static

friction for the box on the floor of the trunk.

(a) 0.42 (d) 0.33

(b) 0.54 (e) This cannot be determined without knowing the mass of

(c) 0.17 the box.

15. In an amusement park ride, a small child stands against the wall of a cylindrical room

that is then made to rotate. The floor drops downward and the child remains pinned

against the wall. If the radius of the device is 2.15 m and the relevant coefficient of

friction between the child and the wall is 0.400, with what minimum speed is the child

moving if he is to remain pinned against the wall?

(a) 7.26 m/s (c) 12.1 m/s (e) 9.80 m/s

(b) 3.93 m/s (d) 5.18 m/s


18. The maximum speed at which a car can safely negotiate an unbanked curve depends

on all of the following factors except

(a) the diameter of the curve.

(b) the acceleration due to gravity.

(c) the coefficient of static friction between the road and the tires.

(d) the coefficient of kinetic friction between the road and the tires.

(e) the ratio of the static frictional force between the road and the tires and the

normal force exerted on the car.

20. Determine the minimum angle at which a roadbed should be banked so that a car

traveling at 20.0 m/s can safely negotiate the curve if the radius of the curve is

2.00 × 102 m.

(a) 0.200° (c) 11.5° (e) 78.2°

(b) 0.581° (d) 19.6°

Questions 23 through 25 pertain to the statement below: A 1000-kg car travels along a straight 500-m portion of highway (from A to B) at a

constant speed of 10 m/s. At B, the car encounters an unbanked curve of radius 50 m. The

car follows the road from B to C traveling at a constant speed of 10 m/s while the

direction of the car changes from east to south.

23. What is the magnitude of the acceleration of the car as it travels from A to B?

(a) 2 m/s2 (c) 10 m/s

2 (e) zero m/s

2

(b) 5 m/s2 (d) 20 m/s

2

24. What is the magnitude of the acceleration of the car as it travels from B to C?

(a) 2 m/s2 (c) 10 m/s

2 (e) zero m/s

2

(b) 5 m/s2 (d) 20 m/s

2

25. What is the magnitude of the frictional force between the tires and the road as the car

negotiates the curve from B to C?

(a) 20 000 N (c) 5000 N (e) 1000 N

(b) 10 000 N (d) 2000 N


26. The earth exerts the necessary centripetal force on an orbiting satellite to keep it

moving in a circle at constant speed. Which statement best explains why the speed of the

satellite does not change although there is a net force exerted on it?

(a) The satellite is in equilibrium.

(b) The acceleration of the satellite is zero m/s2.

(c) The centripetal force has magnitude mv2/r.

(d) The centripetal force is canceled by the reaction force.

(e) The centripetal force is always perpendicular to the velocity.

30. A satellite is placed in equatorial orbit above Mars, which has a radius of 3397 km

and a mass MM = 6.40 × 1023 kg. The mission of the satellite is to observe the Martian

climate from an altitude of 488 km. What is the orbital period of the satellite?

(a) 9.18 × 102

s (c) 7.36 × 103 s (e) 7.27 × 10

12 s

(b) 3.62 × 103 s d) 1.08 × 10

5 s

45. A 25-kg box is sliding down an ice-covered hill. When it

reaches point A, the box is moving at 11 m/s. Point A is at the

bottom of a circular arc that has a radius R = 7.5 m. What is the

magnitude of the normal force on the box at Point A?

(a) 250 N (d) 650 N

(b) 280 N (e) 900 N

(c) 400 N


Questions 49 through 52 pertain to the situation described below: A 1500-kg car travels at a constant speed of 22 m/s around a circular track that has a

radius of 85 m.

49. Which statement is true concerning this car?

(a) The velocity of the car is changing.

(b) The car is characterized by constant velocity.

(c) The car is characterized by constant acceleration.

(d) The car has a velocity vector that points along the radius of the circle.

(e) The car has an acceleration vector that is tangent to the circle at all times.

50. What is the magnitude of the acceleration of the car?

(a) 5.7 m/s2 (c) 9.8 m/s

2 (e) zero m/s

2

(b) 0.26 m/s2 (d) 1.2 m/s

2

51. What is the average velocity of the car during one revolution?

(a) 8.0 m/s (c) 26 m/s (e) zero m/s

(b) 12 m/s (d) 44 m/s

52. Determine the magnitude of the net force that acts on the car.

(a) 390 N (c) 8.5 × 103 N (e) zero newtons

(b) 1800 N (d) 1.5 × 104 N

53. Jupiter has a mass that is roughly 320 times that of the Earth and a radius equal to 11

times that of the Earth. What is the acceleration due to gravity on the surface of Jupiter?

(a) 2.7 m/s2 (c) 26 m/s

2 (e) 260 m/s

2

(b) 9.8 m/s2 (d) 87 m/s

2


Physics 1401

Chapter 6 Review - Energy

1.

In which one of the following situations is zero net work done?

(a) A ball rolls down an inclined plane.

(b) A physics student stretches a spring.

(c) A projectile falls toward the surface of Earth.

(d) A box is pulled across a rough floor at constant velocity.

(e) A child pulls a wagon across a rough surface causing it to accelerate.

3. A concrete block is pulled 7.0 m across a

frictionless surface by means of a rope. The

tension in the rope is 40 N; and the net work

done on the block is 247 J.

What angle does the rope make with the

horizontal?

(a) 28° (c) 47° (e) 88°

(b) 41° (d) 62°

6.

A force of magnitude 25 N directed at an angle of 37° above the horizontal moves a 10-

kg crate along a horizontal surface at constant velocity. How much work is done by this

force in moving the crate a distance of 15 m?

(a) zero joules (c) 40 J (e) 300 J

(b) 1.7 J (d) 98 J


7. A constant force of 25 N is applied as shown

to a block which undergoes a displacement of

7.5 m to the right along a frictionless surface

while the force acts. What is the work done by

the force?

(a) zero joules (c) −94 J (e) −−−−160 J

(b) +94 J (d) +160 J

11. Which one of the following statements concerning kinetic energy is true?

(a) It can be measured in watts.

(b) It is always equal to the potential energy.

(c) It is always positive.

(d) It is a quantitative measure of inertia.

(e) It is directly proportional to velocity.

15.

The kinetic energy of a car is 8 ⋅ 106 J as it travels along a horizontal road. How much

work is required to stop the car in 10 s?

(a) zero joules (c) 8 ⋅ 105 J (e) 8 ⋅ 10

7 J

(b) 8 ⋅ 104 J (d) 8 ⋅ ⋅ ⋅ ⋅ 10

6 J


18. A 10.0-g bullet traveling horizontally at 755 m/s strikes a stationary target and stops

after penetrating 14.5 cm into the target. What is the average force of the target on the

bullet?

(a) 1.97 ⋅ ⋅ ⋅ ⋅ 104 N (c) 6.26 ⋅ 10

3 N (e) 3.93 ⋅ 10

4 N

(b) 2.07 ⋅ 105 N (d) 3.13 ⋅ 10

4 N

22.

An elevator supported by a single cable descends a shaft at a constant speed. The only

forces acting on the elevator are the tension in the cable and the gravitational force.

Which one of the following statements is true?

(a) The magnitude of the work done by the tension force is larger than that done by the

gravitational force.

(b) The magnitude of the work done by the gravitational force is larger than that done by

the tension force.

(c) The work done by the tension force is zero joules.

(d) The work done by the gravitational force is zero joules.

(e) The net work done by the two forces is zero joules.

24.

A 1500-kg elevator moves upward with constant speed through a vertical distance of 25

m. How much work was done by the tension in the cable?

(a) 990 J (c) 140 000 J (e) 430 000 J

(b) 8100 J (d) 370 000 J


26. Two balls of equal size are dropped from the same height from the roof of a building.

One ball has twice the mass of the other. When the balls reach the ground, how do the

kinetic energies of the two balls compare?

(a) The lighter one has one fourth as much kinetic energy as the other does.

(b) The lighter one has one half as much kinetic energy as the other does.

(c) The lighter one has the same kinetic energy as the other does.

(d) The lighter one has twice as much kinetic energy as the other does.

(e) The lighter one has four times as much kinetic energy as the other does.

28. A woman stands on the edge of a cliff and throws a stone vertically downward with an

initial speed of 10 m/s. The instant before the stone hits the ground below, it has 450 J

of kinetic energy. If she were to throw the stone horizontally outward from the cliff with

the same initial speed of 10 m/s, how much kinetic energy would it have just before it

hits the ground?

(a) 50 J (c) 450 J (e) 950 J

(b) 100 J (d) 800 J

30.

A block is dropped from a high tower and is falling freely under the influence of

gravity. Which one of the following statements is true concerning this situation? Neglect

air resistance.

(a) As the block falls, the net work done by all of the forces acting on the block is zero

joules.

(b) The kinetic energy increases by equal amounts over equal distances.

(c) The kinetic energy of the block increases by equal amounts in equal times.

(d) The potential energy of the block decreases by equal amounts in equal times.

(e) The total energy of the block increases by equal amounts over equal distances.

Questions 37 and 38 pertain to the situation described below:


A 2.0-kg projectile is fired with initial velocity components vox = 30 m/s and voy = 40 m/s

from a point on the earth's surface. Neglect any effects due to air resistance.

37. What is the kinetic energy of the projectile when it reaches the highest point in its

trajectory?

(a) zero joules (c) 1600 J (e) 4900 J

(b) 900 J (d) 2500 J

38.

How much work was done in firing the projectile?

(a) 900 J (c) 2500 J (e) 9800 J

(b) 1600 J (d) 4900 J


39. Two boxes are connected to each other as

shown. The system is released from rest and

the 1.00-kg box falls through a distance of

1.00 m. The surface of the table is frictionless.

What is the kinetic energy of box B just before

it reaches the floor?

(a) 2.45 J (d) 29.4 J

(b) 4.90 J (e) 39.2 J

(c) 9.80 J

42.

A bicyclist is traveling at a speed of 20.0 m/s as he approaches the bottom of a hill. He

decides to coast up the hill and stops upon reaching the top. Determine the vertical

height of the hill.

(a) 28.5 m (c) 11.2 m (e) 20.4 m

(b) 3.70 m (d) 40.8 m

45. An engineer is asked to design a playground slide such that the speed a child reaches at

the bottom does not exceed 6.0 m/s. Determine the maximum height that the slide can

be.

(a) 1.8 m (c) 3.2 m (e) 14 m

(b) 2.9 m (d) 4.5 m


50.

The initial velocity of a 4.0-kg box is 11 m/s, due west. After the box slides 4.0 m

horizontally, its speed is 1.5 m/s. Determine the magnitude and the direction of the non-

conservative force acting on the box as it slides.

(a) 42 N, due west (c) 31 N, due east (e) 83 N, due west

(b) 120 N, due east (d) 59 N, due east

51. An automobile approaches a barrier at a speed of 20 m/s along a level road. The driver

locks the brakes at a distance of 50 m from the barrier. What minimum coefficient of

kinetic friction is required to stop the automobile before it hits the barrier?

(a) 0.4 (c) 0.6 (e) 0.8

(b) 0.5 (d) 0.7


55.

A 51-kg woman runs up a flight of stairs in 5.0 s. Her net upward displacement is 5.0 m.

Approximately, what average power did the woman exert while she was running?

(a) 5.0 kW (c) 0.75 kW (e) 0.25 kW

(b) 1.0 kW (d) 0.50 kW

57. An escalator is 30.0 meters long and slants at 30.0° relative to the horizontal. If it moves

at 1.00 m/s, at what rate does it do work in lifting a 50.0 kg man from the bottom to the

top of the escalator?

(a) 49.3 W (c) 245 W (e) 495 W

(b) 98.0 W (d) 292 W

59. A warehouse worker uses a forklift to lift a crate of pickles on a platform to a height

2.75 m above the floor. The combined mass of the platform and the crate is 207 kg. If

the power expended by the forklift is 1440 W, how long does it take to lift the crate?

(a) 37.2 s (c) 3.87 s (e) 1.86 s

(b) 5.81 s (d) 18.6 s


61. The amount on energy needed to power a 0.10-kW bulb for one minute would be just

sufficient to lift a 1.0-kg object through a vertical distance of

(a) 12 m (c) 100 m (e) 610 m

(b) 75 m (d) 120 m

62. The graph shows the force component along the

displacement as a function of the magnitude of

the displacement. Determine the work done by

the force during the interval from 2 to 10 m.

(a) 140 J

(b) 190 J

(c) 270 J

(d) 450 J

(e) 560 J


67. A motorist driving a 1000-kg car wishes to increase her speed from 20 m/s to 30 m/s in

5 s. Determine the horsepower required to accomplish this increase. Neglect friction.

(a) 20 hp (c) 70 hp (e) 90 hp

(b) 30 hp (d) 80 hp


Physics 1401

Chapter 7N Review-New

CHAPTER 6

2.

A rock is dropped from a high tower and falls freely under the influence of gravity.

Which one of the following statements is true concerning the rock as it falls?

(a) It will gain an equal amount of momentum during each second.

(b) It will gain an equal amount of kinetic energy during each second.

(c) It will gain an equal amount of speed for each meter through which it falls.

(d) It will gain an equal amount of momentum for each meter through which it falls.

(e) The amount of momentum it gains will be proportional to the amount of potential

energy that it loses.

3. 3. A stunt person jumps from the roof of a tall building, but no injury occurs because the

person lands on a large, air-filled bag. Which one of the following best describes why

no injury occurs?

(a) The bag provides the necessary force to stop the person.

(b) The bag reduces the impulse to the person.

(c) The bag increases the amount of time the force acts on the person and reduces the

change in momentum.

(d) The bag decreases the amount of time during which the momentum is changing and

reduces the average force on the person.

(e) The bag increases the amount of time during which the momentum is changing

and reduces the average force on the person.

5. A 1.0-kg ball has a velocity of 12 m/s downward just before it strikes the ground and

bounces up with a velocity of 12 m/s upward. What is the change in momentum of the

ball?

(a) zero kg • m/s (c) 12 kg • m/s, upward (e) 24 kg • m/s, upward

(b) 12 kg • m/s, downward (d) 24 kg • m/s, downward


9.

A 0.065-kg tennis ball moving to the right with a speed of 15 m/s is struck by a tennis

racket, causing it to move to the left with a speed of 15 m/s. If the ball remains in

contact with the racquet for 0.020 s, what is the magnitude of the average force

experienced by the ball?

(a) zero newtons (c) 160 N (e) 9.8 ⋅ 104 N

(b) 98 N (d) 1.6 ⋅ 105 N

12. While a car is stopped at a traffic light in a storm, raindrops strike the roof of the car.

The area of he roof is 5.0 m2. Each raindrop has a mass of 3.7 ⋅ 10

–4 kg and speed of 2.5

m/s before impact and is at rest after the impact. If, on average at a given time, 150

raindrops strike each square meter, what is the impulse of the rain striking the car?

(a) 0.69 N • s (c) 0.14 N • s (e) 21 N • s

(b) 0.046 N • s (d) 11 N • s

15. A football player kicks a 0.41-kg football initially at rest; and the ball flies through the

air. If the kicker’s foot was in contact with the ball for 0.051 s and the ball’s initial

speed after the collision is 21 m/s, what was the magnitude of the average force on the

football?

(a) 9.7 N (c) 81 N (e) 210 N

(b) 46 N (d) 170 N


Questions 16 and 17 pertain to the situation described below: A 4.0-kg block slides along a frictionless surface with a constant speed of 5.0 m/s. Two

seconds after it begins sliding, a horizontal, time-dependent force is applied to the mass.

The force is removed eight seconds later. The graph shows how the force on the block

varies with time.

16.

What is the magnitude of the total impulse of the force acting on the block?

(a) 20 N • s (c) 48 N • s (e) 60 N • s

(b) 42 N • s (d) 54 N • s

17. What, approximately, is the speed of the block at t = 11 seconds?

(a) 5.0 m/s (c) 25 m/s (e) 75 m/s

(b) 16 m/s (d) 65 m/s

21. A 50-kg toboggan is coasting on level snow. As it passes beneath a bridge, a 20-kg

parcel is dropped straight down and lands in the toboggan. If (KE)1 is the original

kinetic energy of the toboggan and (KE)2 is the kinetic energy after the parcel has been

added, what is the ratio (KE)2/(KE)1.

(a) 0.4 (c) 0.7 (e) 1

(b) 0.6 (d) 0.8


Ans. c.

25.

An 80-kg astronaut carrying a 20-kg tool kit is initially drifting toward a stationary

space shuttle at a speed of 2 m/s. If she throws the tool kit toward the shuttle with a

speed of 6 m/s as seen from the shuttle, her final speed is

(a) 1 m/s toward the shuttle. (d) 4 m/s toward the shuttle.

(b) 1 m/s away from the shuttle. (e) 6 m/s away from the shuttle.

(c) 2 m/s toward the shuttle.

28. Two objects of equal mass traveling toward each other with equal speeds undergo a

head on collision. Which one of the following statements concerning their velocities

after the collision is necessarily true?

(a) They will exchange velocities. (d) Their velocities will be zero.

(b) Their velocities will be reduced. (e) Their velocities may be zero.

(c) Their velocities will be unchanged.


31. Complete the following statement: Momentum will be conserved in a two-body

collision only if

(a) both bodies come to rest.

(b) the collision is perfectly elastic.

(c) the kinetic energy of the system is conserved.

(d) the net external force acting on the two-body system is zero.

(e) the internal forces of the two body system cancel in action-reaction pairs.

39.

A 50.0-kg boy runs at a speed of 10.0 m/s and jumps onto a cart as shown in the figure.

The cart is

initially at rest.

If the speed of the cart with the boy on it is 2.50 m/s, what is the mass of the cart?

(a) 150 kg (c) 210 kg (e) 300 kg

(b) 175 kg (d) 260 kg


42. A 35-kg girl is standing near and to the left of a 43-kg boy on the frictionless surface of

a frozen pond. The boy tosses a 0.75-kg ice ball to the girl with a horizontal speed of 6.2

m/s. What are the velocities of the boy and the girl immediately after the girl catches the

ice ball?

girl boy

(a) 0.81 m/s, left 0.67 m/s, right

(b) 0.17 m/s, left 0.14 m/s, left

(c) 0.18 m/s, right 0.13 m/s, left

(d) 0.42 m/s, left 0.49 m/s, right

(e) 0.13 m/s, left 0.11 m/s, right

50. In the game of billiards, all the balls have

approximately the same mass, about 0.17 kg.

In the figure, the cue ball strikes another ball

such that it follows the path shown. The other

ball has a speed of 1.5 m/s immediately after

the collision. What is the speed of the cue

ball after the collision?

(a) 1.5 m/s (c) 2.6 m/s (e) 5.2 m/s

(b) 1.8 m/s (d) 4.3 m/s

64. A 100-kg fisherman and a 500-kg supply crate are on a frozen pond that is essentially

frictionless. The man and the crate are initially separated by a distance of 600 meters.

The fisherman uses a very light rope to pull the crate closer to him. How far has the man

moved when the crate reaches the fisherman?

(a) zero meters (c) 50 m (e) 500 m

(b) 10 m (d) 100 m


Physics 1401

Chapter 8 Review

2. A wrench is used to tighten a nut as shown in

the figure. A 12-N force is applied 7.0 cm

from the axis of rotation. What is the torque

due to the applied force?

(a) 0.58 N • m

(b) 0.84 N • m

(c) 1.71 N • m

(d) 14 N • m

(e) 58 N • m

3. A string is tied to a doorknob 0.79 m from the

hinge as shown in the figure. At the instant

shown, the force applied to the string is 5.0 N.

What is the torque on the door?

(a) 3.3 N • m

(b) 2.2 N • m

(c) 1.1 N • m

(d) 0.84 N • m

(e) 0.40 N • m


6. A horizontal, 10-m plank weighs 100 N. It

rests on two supports that are placed 1.0

m from each end as shown in the figure.

How close to one end can an 800-N

person stand without causing the plank to

tip?

(a) 0 m (d) 0.6 m

(b) 0.2 m (e) 0.8 m

(c) 0.5 m

8. One end of a rope is tied to the handle of a

horizontally-oriented and uniform door. A force F is

applied to the other end of the rope as shown in the

drawing. The door has a weight of 145 N and is

hinged on the right. What is the maximum magnitude

of F at which the door will remain at rest?

(a) 145 N (d) 424 N

(b) 265 N (e) 530 N

(c) 381 N


10. 10. In the drawing shown, the large wheel has a radius of 8.5

m. A rope is wrapped around the edge of the wheel and a

7.6 kg-box hangs from the rope. A smaller disk of radius

1.9 m is attached to the wheel. A rope is wrapped around

the edge of the disk as shown. An axis of rotation passes

through the center of the wheel-disk system. What is the

value of the mass M that will prevent the wheel from

rotating?

(a) 1.7 kg (d) 34 kg

(b) 3.8 kg (e) 46 kg

(c) 12 kg

14. Consider four point masses located as shown in the

sketch. The acceleration due to gravity is the same

everywhere. What is the x coordinate of the center of

gravity for this system?

(a) 2.0 m (c) 3.0 m (e) 3.8 m

(b) 2.7 m (d) 3.3 m


17. Consider the following four objects:

a hoop; a solid sphere; a flat disk; a hollow sphere

Each of the objects has mass M and radius R. The axis of rotation passes through the

center of each object, and is perpendicular to the plane of the hoop and the plane of

the flat disk. Which object requires the largest torque to give it the same angular

acceleration ?

(a) the hoop (d) the hollow sphere

(b) the flat disk (e) both the solid and the hollow spheres

(c) the solid sphere

20. A massless frame in the shape of a square with 2-m sides

has a 1-kg ball at each corner. What is the moment of

inertia of the four balls about an axis through the corner

marked O and perpendicular to the plane of the paper?

(a) 4 kg • m2

(b) 8 kg • m2

(c) 10 kg • m2

(d) 12 kg • m2

(e) 16 kg • m2


22. The drawing shows the top view of a door that

is 2 m wide. Two forces are applied to the door

as indicated. What is the magnitude of the net

torque on the door with respect to the hinge?

(a) 0 N • m (c) 8.7 N • m (e) 26.0 N • m

(b) 5.0 N • m (d) 10.0 N • m

26. Three children are pulling on a rotatable platform on a

playground. The platform has a radius of 3.65 m. In the

picture, two children are pulling with equal forces of

40.0 N in an attempt to make the platform rotate

clockwise. The third child applies a force of 60 N as

shown. What is the net torque on the platform?

Note: “ccw” is counterclockwise and “cw” is

clockwise.

(a) 73 N • m, ccw (c) 511 N • m, ccw (e) 0 N • m

(b) 73 N • m, cw (d) 511 N • m, cw


28. A 45-N brick is suspended by a light string from a 2.0-kg

pulley. The brick is released from rest and falls to the

floor below as the pulley rotates through 5.0 rad. The

pulley may be considered a solid disk of radius 1.5 m.

What is the angular speed of the pulley?

(a) 7.3 rad/s (d) 15 rad/s

(b) 8.1 rad/s (e) 17 rad/s

(c) 9.4 rad/s

31. Consider the following three objects, each of the same mass and radius:

(1) a solid sphere (2) a solid disk (3) a hoop

All three are released from rest at the top of an inclined plane. The three objects

proceed down the incline undergoing rolling motion without slipping. In which order

do the objects reach the bottom of the incline?

(a) 1, 2, 3 (c) 3, 1, 2 (e) All three reach the bottom

(b) 2, 3, 1 (d) 3, 2, 1 at the same time.

34. A 2.0-kg solid cylinder of radius 0.5 m rotates at a rate of 40 rad/s about its

cylindrical axis. What power is required to bring the cylinder to rest in 10 s?

(a) 20 W (c) 160 W (e) 400 W

(b) 40 W (d) 200 W


38. A ceiling fan has five blades, each with a mass of 0.34 kg and a length of 0.66 m.

The fan is operating in its “low” setting at which the angular speed is 9.4 rad/s. If the

blades can be approximated as uniform thin rods that rotate about one end, what is

the total rotational kinetic energy of the five blades?

(a) 35 J (c) 23 J (e) 11 J

(b) 29 J (d) 17 J

41. What happens when a spinning ice skater draws in her outstretched arms?

(a) Her angular momentum decreases.

(b) Her angular momentum increases.

(c) Her moment of inertia decreases causing her to speed up.

(d) Her moment of inertia decreases causing her to slow down.

(e) The torque that she exerts increases her moment of inertia.

44. A 1500-kg satellite orbits a planet in a circular orbit of radius 6.2 × 106 m. What is

the angular momentum of the satellite in its orbit around the planet if the satellite

completes one orbit every 1.5 × 104 s?

(a) 3.9 × 106 kg • m

2/s (c) 6.2 × 10

8 kg • m

2/s (e) 2.4 × 10

13 kg • m

2/s

(b) 1.4 × 1014

kg • m2/s (d) 8.1 × 10

11 kg • m

2/s


50. A 3.0-kg ball moves in a straight line at 10 m/s as

shown in the figure. At the instant shown, what is

its angular momentum about the point P?

(a) 30 kg • m2/s

(b) 90 kg • m2/s

(c) 120 kg • m2/s

(d) 150 kg • m2/s

(e) zero kg • m2/s

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