Deck 4: Forces and Motion I: Newtons Laws

Question 1

A force accelerates a body of mass M. A second body requires half as much force to produce twice the acceleration. What is the mass of the second body?

A) M
B) 2M
C) M/2
D) 4M
E) M/4

Answer 1

4M

Question 2

A net force is exerted toward the east on an object that is initially at rest. In which direction does the object start to move?

A) north
B) east
C) west
D) south
E) It may start to move in any of these directions.

Answer 2

east

Question 3

A force F produces an acceleration a on an object of mass m. A force 3F is exerted on a second object, and an acceleration 8a results. What is the mass of the second object?

A) 3m
B) 9m
C) 24m
D) 3/8)m
E) 8/3)m

Answer 3

3/8)m

Question 4

A force accelerates a body of mass M. A second body requires twice as much force to produce the same acceleration. What is the mass of the second body?

A) M
B) 2M
C) M/2
D) 4M
E) M/4

Question 5

A net force of 64 N acts on a mass of 16 kg. The resulting acceleration is

A) 16 m/s².
B) 0.51 m/s².
C) 64 m/s².
D) 9.0 m/s².
E) 4.0 m/s².

Question 6

A 10-N force is applied to mass M. The same force is applied to mass 4M. The ratio of the acceleration of the smaller mass to the acceleration of the larger mass is

A) 4 to 1.
B) 20 to 1.
C) 1 to 1.
D) 1 to 2.
E) 1 to 4.

Question 7

A mass m is traveling at an initial speed of 25.0 m/s. It is brought to rest in a distance of 62.5 m by a net force of 15.0 N. The mass is

A) 37.5 kg.
B) 3.00 kg.
C) 1.50 kg.
D) 6.00 kg.
E) 3.75 kg.

Question 8

If you apply the same net force to objects with masses M and 4M, the acceleration of the mass M is

A) the same as for the mass 4M.
B) four times the acceleration of the mass 4M.
C) one-fourth the acceleration of the mass 4M.
D) twice the acceleration of the mass 4M.
E) one-half the acceleration of the mass 4M.

Question 9

A net force is exerted on an object toward the north. The object

A) is moving toward the north.
B) is moving toward the east.
C) is moving toward the west.
D) is moving toward the south.
E) may be moving in any direction.

Question 10

A 3.00 kg mass is traveling at an initial speed of 25.0 m/s. What is the magnitude of the force required to bring the mass to rest in a distance of 62.5 m?

A) 7.50 N
B) 3.00 N
C) 15.0 N
D) 62.5 N
E) 37.5 N

Question 11

A force accelerates a body of mass M. The same force applied to a second body produces three times the acceleration. What is the mass of the second body?

A) M
B) 3M
C) M/3
D) 9M
E) M/9

Question 12

A mass of 25 kg is acted on by two forces, one of which is 10 N due east while the second one is 15 N due north. The acceleration of the mass is

A) 0.72 m/ s², 56.3^o north of east.
B) 0.20 m/ s², due east.
C) 0.72 m/ s², 33.7 ^o north of east.
D) 1.0 m/ s², 33.7 ^o north of east.
E) 0.20 m/ s², 56.3 ^o north of east.

Question 13

If you want the same acceleration with masses M and 4M, the force applied on the mass M is

A) the same as for the mass 4M.
B) four times the force applied on the mass 4M.
C) one-fourth the force applied on the mass 4M.
D) twice the force applied on the mass 4M.
E) one-half the force applied on the mass 4M.

Question 14

A ball of mass 2.0 kg is acted on by two forces, and . The magnitude of the acceleration is

A) 2.5 m/s².
B) 3.9 m/s².
C) 4.6 m/s².
D) 5.1 m/s².
E) 5.8 m/s².

Question 15

A particle with a mass of 200 g is acted on by a net force of 4.5 N. The acceleration of the particle is

A) 90 cm/s².
B) 2.3 cm/s².
C) 0.90 km/s².
D) 23 m/s².
E) 9.0 m/s².

Question 16

A mass of 25 kg is acted on by two forces, one of which is 15 N due east while the second one is 10 N due north. The acceleration of the mass is

A) 0.72 m/ s², 56.3^o north of east.
B) 0.20 m/ s², due east.
C) 0.72 m/ s², 33.7 ^o north of east.
D) 1.0 m/ s², 33.7 ^o north of east.
E) 0.20 m/ s², 56.3 ^o north of east.

Question 17

A ball of mass 2.0 kg is acted on by two forces , and . The acceleration vector, , of the mass is in m/s²)

A) .
B) .
C) .
D) .
E) .

Question 18

A third force is applied on the object so that the net force on the object is zero. Which force vector best represents the third force?

A) 1)
B) 2)
C) 3)
D) 4)
E) none of the vectors

Question 19

A ball of mass 2.0 kg is acted on by two forces, , and . The direction of the acceleration vector ) w.r.t to the +x-axis is

A) .
B) .
C) .
D) .
E) .

Question 20

An object is moving to the right at a constant speed. Which one of the following statements must be correct?

A) No forces are acting on the object.
B) A larger number of forces are acting on the object to the right than to the left.
C) The net force acting on the object is to the right.
D) No net force is acting on the object.
E) Just one force is acting on the object, and it is acting downward.

Question 21

The force needed to accelerate the rover Opportunity on Mars at 1 m/s² in the horizontal direction is ____ the force needed to accelerate the rover while it was undergoing testing on Earth.

A) less than
B) equal to
C) greater than
D) Unable to tell
E) dependent on what g is on Mars

Question 22

The SI unit of force is the

A) newton.
B) gram.
C) pound.
D) kilogram.
E) None of these is correct.

Question 23

An unknown force is applied to two unknown masses M_A and M_B. Their accelerations and are measured. From these data we can determine

A) the magnitude of only.
B) M_A and M_B only.
C) the magnitudes of , M_A, and M_B only.
D) the ratio of M_A to M_B only.
E) M_A, M_B, and the weights of M_A and M_B.

Question 24

According to Newton's law of inertia,

A) objects moving with an initial speed relative to a given frame of reference eventually come to rest relative to the reference frame.
B) whether an object is at rest or is moving with constant velocity depends on the inertial reference frame in which the object is observed.
C) rest is the most natural state of motion.
D) an object at rest in a given frame of reference eventually finds itself in motion relative to the frame of reference.
E) forces always exist in pairs.

Question 25

The diagrams below show the application of a net force F on a block of mass m. Which diagrams) produces the largest acceleration on the block in the horizontal direction?

A) 1) and 3)
B) 2)
C) 3)
D) 2) and 4)
E) The acceleration is the same for all four.

Question 26

If force in N), length in m), and time in s) were considered to be the fundamental quantities, the units of mass would be

A) s²/N · m).
B) m · s.
C) N² · m/s².
D) N · s²/m.
E) m/N.

Question 27

A body is sent out in space. Which of the following statements is true of this body as it moves away from Earth?

A) The body's mass and weight remain equal.
B) The body's mass remains constant, and its weight decreases.
C) The body's mass decreases, and its weight remains constant.
D) The body's mass and weight decrease.
E) The body's mass decreases, and its weight increases.

Question 28

An inertial reference frame is one in which

A) Newton's first law describes the behavior of matter.
B) the law of inertia is not applicable.
C) there is a great deal of matter.
D) the object of interest is traveling in a circular path.
E) forces do not necessarily exist in pairs.

Question 29

The mass of a body that weighs 2.00 N at sea level is

A) 0.204 kg.
B) 2.00 kg,
C) 19.6 kg,
D) 9.80 kg.
E) 0.451 kg.

Question 30

A physical quantity that is sometimes described as the measure of the resistance of a body to a change in its motion is

A) force.
B) mass.
C) acceleration.
D) weight.
E) friction.

Question 31

Which of the following statements includes all the essential elements of Newton's first law?

A) A body at rest persists in its state of rest unless acted on by a nonzero net external force.
B) A body persists in its state of rest or of uniform motion in a straight line as long as the net external force remains constant.
C) For every action there is an equal and opposite reaction.
D) A body persists in its state of rest or of uniform motion in a straight line unless acted on by a nonzero net external force.
E) The acceleration of a body is proportional to the net external force acting on it and to the mass of the body.

Question 32

Newton's law of inertia does not describe the behavior of objects that are

A) in inertial frames of reference.
B) moving with constant velocity relative to a given frame of reference.
C) at rest relative to a given frame of reference.
D) moving in accelerated frames of reference.
E) moving in a straight line at constant speed relative to a given reference frame.

Question 33

A body moves with constant speed in a straight line. Which of the following statements must be true?

A) No force acts on the body.
B) A single constant force acts on the body in the direction of motion.
C) A single constant force acts on the body in the direction opposite to the motion.
D) A net force of zero acts on the body.
E) A constant net force acts on the body in the direction of motion.

Question 34

Which of the following is a unit of force?

A) m²/s²
B) kg · s²/m
C) kg · m/s²
D) N · s
E) N/kg

Question 35

An astronaut lands on an Earthlike planet and drops a small lead ball with a mass of 76.5 g from the top of her spaceship. The point of release is 18 m above the surface of the planet and the ball takes 2.5 s to reach the ground. The astronaut's mass on Earth is 68.5 kg. Her weight on the planet is

A) 69.0 N.
B) 395 N.
C) 670 N.
D) 990 N.
E) 1.02 kN.

Question 36

An object moves with constant speed in a straight line. Which of the following statements can be true according to Newton's laws of motion? I. No force is acting. II. Only one nonzero force is acting.III. Two nonzero forces are acting. IV. Three nonzero forces are acting.

A) Only I.
B) Only I and II.
C) Only II and III.
D) Only I, III, and IV.
E) Only II, III, and IV.

Question 37

When Newton's first law of motion is mentioned, you should immediately think of

A) .
B) action-and-reaction forces.
C) inertia.
D) gravitational forces.
E) centripetal acceleration.

Question 38

Which of the following statements is true?

A) The mass of a body is a quantitative measure of its inertia.
B) Mass is a vector quantity.
C) The mass of a body is directly proportional to the acceleration it is experiencing.
D) The unit of mass in the U.S. customary system is the newton.
E) The mass of a body is inversely proportional to the resultant force acting on it.

Question 39

The weight of an object is

A) the same as the mass of the object.
B) the quantity of matter in the object.
C) the mass of the object multiplied by the acceleration due to gravity at sea level, regardless of where the object is located.
D) the result of the gravitational force acting on the object.
E) the reading on a spring scale attached to the object.

Question 40

Which of the following is not a unit of force?

A) newton
B) pound
C) slug
D) dyne
E) kg · m/s²

Question 41

An astronaut lands on an Earthlike planet and drops a small lead ball with a mass of 76.5 g from the top of her spaceship. The point of release is 18 m above the surface of the planet and the ball takes 2.5 s to reach the ground. The astronaut's mass on Earth is 68.5 kg. Her mass on the planet is

A) 68.5 kg.
B) 395 kg.
C) 670 kg,
D) 99.0 kg.
E) 40.2 kg.

Question 42

You want to elope by sliding down a nylon rope made by tying stockings together. The rope will withstand a maximum tension of 300 N without breaking. Your mass is 61.2 kg. The magnitude of the smallest acceleration a with which you can slide down the rope is

A) 9.81 m/s².
B) 4.91 m/s².
C) zero.
D) 2.40 m/s².
E) 19.6 m/s².

Question 43

The diagrams below show the application of an external force F on a block of mass m resting on a horizontal surface. In which diagrams) does the block experience the largest normal force?

A) Both 1) and 3)
B) Only 1)
C) Only 2)
D) Only 3)
E) Only 4)

Question 44

A particle of mass 1.3 kg is sliding down a frictionless slope inclined at 30^o to the horizontal. The acceleration of the particle down the slope is

A) 1.3 m/s².
B) 9.8 m/s².
C) 0.5 m/s².
D) 8.5 m/s².
E) 4.9 m/s².

Question 45

What is the weight of a 50-kg boy on the Moon, where the acceleration due to gravity is 1.6 m/s²?

A) 80 N
B) 100 N
C) 490 N
D) 50 N
E) 80 lbs

Question 46

The diagrams below show the application of an external force F on a block of mass m resting on a horizontal surface. In which diagrams) does the block experience the smallest normal force?

A) Both 1) and 3)
B) Only 1)
C) Only 2)
D) Only 3)
E) Only 4)

Question 47

Which of the following free-body diagrams represents the car going uphill at a constant speed?

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 48

In a crash test, the strapped-in 75-kg dummy moves a distance of 0.80 m when the test car is slammed straight into a wall at 11.2 m/s ~25 mph). The average force acting on the dummy during the collision is how many times his own weight?

A) 0.13
B) 78
C) 0.71
D) 8.0
E) 4.0

Question 49

A boy sits in a tire that is attached to a rope that passes over a pulley fastened to the ceiling and then passes back down to the boy's hands. The weight of the boy plus the tire is W. The force with which the boy must pull on the free end of the rope to support his weight in the tire is

A) 1/2)W.
B) W.
C) 2W.
D) 2/3)W.
E) 3/2)W.

Question 50

A vertical rope is attached to an object that has a mass of 40.0 kg and is at rest. The tension in the rope needed to give the object an upward speed of 3.50 m/s in 0.700 s is

A) 592 N.
B) 390 N.
C) 200 N.
D) 980 N.
E) 720 N.

Question 51

A car is accelerating horizontally at a rate of 2.5 m/s². A mass of 250 g is hanging from the ceiling on a string 1.2 m long. The angle that the string makes with the vertical is

A) 14.3^o toward the back of the car.
B) 76^o toward the back of the car.
C) 7^o toward the front of the car.
D) 14.3^o toward the front of the car.
E) 0^o, or straight down.

Question 52

A 44.5-N weight is hung on a spring scale, and the scale is hung on a string. The string is lowered at a rate such that the entire assembly has a downward acceleration of 4.90 m/s². The scale reads

A) 0 N.
B) 22.2 N.
C) 44.5 N.
D) 66.7 N.
E) 71.2 N.

Question 53

Of the following values, which is most nearly equal to the weight of a 1-kg body?

A) 1 N
B) 103 dynes
C) 2.2 lbs
D) 0.454 lbs
E) 2.2 N

Question 54

We all know it makes sense to bend one's knees when dropping from a height.Suppose a very silly 70-kg person were instead to drop down from a height of 1.4 m onto the ground and stop stiffly within a distance of only 0.60 cm. Calculate how many times his own weight is the average force his body feels.

A) 15
B) 24
C) 2.3 * 10³
D) 6.1 *10²
E) 2.3 *10²

Question 55

Which of the following free-body diagrams represents the car going downhill without acceleration?

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 56

Which of the following free-body diagrams represents the block sliding down a frictionless inclined plane?

A) 1)
B) 2)
C) 3)
D) 4)
E) 5)

Question 57

A horse-drawn coach is decelerating at 3.0 m/s² while moving in a straight line horizontally. A 350-g mass is hanging on a string 1.6 m long from the ceiling of the coach. The angle that the string makes with the vertical is

A) 9.3^o toward the front of the coach.
B) 17^o toward the front of the coach.
C) 9.3^o toward the back of the coach.
D) 2.5^o toward the front of the coach.
E) 0^o, or straight down.

Question 58

Which of the following is not a unit of mass?

A) pound
B) kilogram
C) gram
D) slug
E) milligram

Question 59

A shopper steps on an escalator moving downward at a constant speed toward the bargain basement in a large department store. On his way down, the normal force exerted on him by the step of the escalator is

A) greater than his weight when he is off the escalator.
B) equal to his weight when he is off the escalator.
C) less than his weight when he is off the escalator.
D) dependent on how fast the escalator is moving.
E) unknown; insufficient information is given to answer correctly.

Question 60

The acceleration due to gravity on the Moon is only about 1/6 of that on Earth. An astronaut whose weight on Earth is 600 N travels to the lunar surface. His mass as measured on the Moon is

A) 600 kg.
B) 100 kg.
C) 61.2 kg.
D) 10.0 kg.
E) 360 kg.

Question 61

An 80-kg man on ice skates pushes a 40-kg boy, also on skates, with a force of 100 N. The force exerted by the boy on the man is

A) 200 N.
B) 100 N.
C) 50 N.
D) 40 N.
E) zero unless the boy pushes back.

Question 62

A fat cat, ever conscious of its weight, walks into an elevator and steps on a scale. The elevator begins to accelerate downward. While the elevator is accelerating, the scale reads

A) more than when the elevator is stationary.
B) more than if the elevator were accelerating upward.
C) less than when the elevator is stationary.
D) a negative value.
E) Insufficient information is given to answer correctly.

Question 63

An object with a mass m = 250 g is on a plane inclined at 30^o above the horizontal and is attached by a string to a mass m = 150 g. There is no friction and mass m hangs freely and is initially at rest. When mass m has descended a distance h = 10 cm, its speed will be

A) 35.0 cm/s.
B) 7.00 cm/s.
C) 140 cm/s.
D) 110 cm/s.
E) 70.0 cm/s.

Question 64

A horse exerts a force F on a cart, causing the cart to move with increasing speed. What force does the cart exert on the horse?

A) zero
B) F
C) greater than F
D) less than F
E) The force cannot be determined unless the acceleration is given.

Question 65

A body of weight w rests on the surface of Earth. What force does the body exert on Earth? Ignore Earth's rotation.)

A) w
B) greater than w
C) less than w
D) 9.81w
E) zero

Question 66

A body of weight w is in free fall near the surface of Earth. What force does the body exert on the Earth?

A) w
B) greater than w
C) less than w
D) 9.81w
E) zero

Question 67

A horse harnessed to a wagon refuses to pull, citing Newton's third law, which states that for every force there is an equal but opposite reaction force. The horse, incorrect in its reasoning, can pull the wagon because

A) after it gives a jerk and the wagon is moving, its pulling force will be greater than the reaction to this force.
B) the law applies only to static cases.
C) the wagon cannot possibly pull back with a force equal in magnitude to the pulling force.
D) the action and reaction forces are acting on different bodies.
E) after friction is overcome, the reaction force is less than the pulling force.

Question 68

A 100-kg man on ice skates pushes a 25-kg boy, also on skates, with a force of 250 N. As a result,

A) both the man and the boy will have an acceleration of magnitude 2 m/s².
B) only the boy will have an acceleration of magnitude 2 m/s².
C) only the man will have an acceleration of magnitude 10 m/s².
D) the man will have an acceleration of magnitude 2.5 m/s².
E) the heavier man will be stationary.

Question 69

A 100-kg man on ice skates pushes a 25-kg boy, also on skates, with a force of 250 N. As a result,

A) both the man and the boy will have an acceleration of magnitude 2 m/s².
B) only the boy will have an acceleration of magnitude 2 m/s².
C) only the man will have an acceleration of magnitude 2 m/s².
D) the boy will have an acceleration of magnitude 10 m/s².
E) the heavier man will be stationary.

Question 70

A boy holds a bird in his hand. The reaction force to the weight of the bird is the force of the

A) Earth on the bird.
B) bird on the Earth.
C) hand on the bird.
D) bird on the hand.
E) Earth on the hand.

Question 71

You are riding an elevator that is accelerating upward at 2.20 m/s². You have a spring balance that is accurately calibrated in newtons. When you hang a mass of 10.0 kg on the balance, the reading of the balance is

A) 120 N.
B) 981 N.
C) 76.0 N.
D) 10.0 N.
E) 9.81 N.

Question 72

A cricket batsman hits a ball with a bat. If the force with which the bat hits the ball is considered the action force, what is the reaction force?

A) The force the bat exerts on the batsman's hands
B) The force on the ball exerted by the hand of the person who catches it
C) The force the ball exerts on the bat
D) The force the bowler exerts on the ball in throwing it
E) Friction as the ball rolls to a stop

Question 73

Two masses, m₁ and m₂, connected by a massless string, are accelerated uniformly on a frictionless surface as shown. The ratio of the magnitude of tensions is given by

A) m₁/m_{2 .}
B) m₂/m_1.
C) m₁ + m₂)/m_{2 .}
D) m₁/m₁ + m₂).
E) m₂/m₁ + m₂).

Question 74

A person of weight w is in an upward-moving elevator when the cable suddenly breaks. What is the person's apparent weight immediately after the elevator starts to fall?

A) w
B) greater than w
C) less than w
D) 9.81w
E) zero

Question 75

A mass 2m is attached by a string to another mass m as illustrated. A force of newtons acts on mass m to accelerate the system. The force in the string, which acts on mass 2m, is

A) 2/3)N.
B) N.
C) 2N.
D) 3N.
E) 3/2)N.

Question 76

A block of mass m is suspended by two strings and is in equilibrium as suggested in the figure above. The tension of the right-hand string divided by the tension of the left-hand string is given by

A) sin $\theta$ ₂ / sin $\theta$ ₁.
B) cos $\theta$ ₁ / cos $\theta$ ₂.
C) cos $\theta$ ₂ / cos $\theta$ ₁.
D) sin $\theta$ ₁ / sin $\theta$ ₂.
E) mg $\theta$ T₁ sin $\theta$ ₁) / T₁ sin $\theta$ ₂).

Question 77

A boy holds a bird in his hand. The reaction force to the normal force exerted on the bird by the boy's hand is the force of

A) the Earth on the bird.
B) the bird on the Earth.
C) the hand on the bird.
D) the bird on the hand.
E) the Earth on the hand.

Question 78

You are riding an elevator that is accelerating downward at 2.20 m/s². You have a spring balance that is accurately calibrated in newtons. When you hang a mass of 10.0 kg on the balance, the reading of the balance is

A) 120 N.
B) 981 N.
C) 76.0 N.
D) 10.0 N.
E) 9.81 N.

Question 79

Rachel has been reading her physics book. She takes her weighing scales into an elevator and stands on them. If her normal weight is 690 N 155 lbs) and the elevator moves upward at 0.25 g and then down at 0.25 g, what is the difference between the up and down scale readings?

A) 690 N
B) 520 N
C) 170 N
D) 345 N
E) 1.04 * 10³ N

Question 80

You are riding an elevator that is in motion. Using a spring balance calibrated in newtons, you notice that a 10.0 kg hanging mass reads 120 N on the scale. What is the acceleration of the elevator?

A) 9.8 m/s² downward
B) 4.9 m/s² upward
C) 2.2 m/s² downward
D) 2.2 m/s² upward
E) 1.1 m/s² downward