Deck 4: Newtons Laws: Explaining Motion

Question 1

A calculus book weighing 20 N rests on the floor of a classroom. The reaction to the force of the floor on the book is a force of

A) 9.8 m/s² exerted by the Earth on the book.
B) 0 N.
C) 2.04 kg exerted by the floor on the book.
D) 20 N exerted by the book on the Earth.

Answer 1

20 N exerted by the book on the Earth.

Question 2

The erroneous idea that an object needs a force on it to keep moving even at constant velocity was held by

A) Aristotle.
B) Galileo.
C) Newton.

Answer 2

Aristotle.

Question 3

A common experience is to find that a steady pull is required to keep an object moving, even on a level surface, when friction is present. Analyzing this experience in light of the laws of motion, the accepted conclusion is that

A) the laws of motion do not apply where there is friction.
B) a frictional force exactly opposes your pull and the first law applies.
C) the object is really accelerating but it is not apparent.
D) your pull is canceled by the third law reaction force.
E) the laws of motion only apply when you start pulling or stop.

Answer 3

a frictional force exactly opposes your pull and the first law applies.

Question 4

A 10-pound sack of potatoes falls from an airplane. As the velocity of the falling sack increases, so does the air resistance on it. When the air resistance equals 10 pounds, the acceleration of the sack will be

A) 100 ft/s².
B) 9.8 m/s.
C) 9.8 m/s².
D) zero.

Question 5

A body sliding on a table is observed to gradually slow down. The correct statement is that the body slows down because

A) no force acts on the body.
B) no net force acts on the body.
C) it is the nature of the body to slow down by itself.
D) a net force acts on the body.

Question 6

A 10.0 kg block on a smooth horizontal surface is acted upon by two forces: a horizontal force of 70 N acting to the left and a horizontal force of 30 N to the right. The acceleration of the block will be

A) 2.3 m/s² to the right.
B) 4.0 m/s² to the right.
C) 10.0 m/s² to the left.
D) 4.0 m/s² to the left.

Question 7

The acceleration of gravity on the Moon's surface is about 1/6 of that on the Earth's surface. An object on the Earth is to be taken to the Moon. We can state that, compared to the Earth,

A) the object's mass and weight will be the same on the Moon.
B) the object's mass will be the same but the weight will be less on the Moon.
C) the object's mass will be less but the weight will be the same on the Moon.
D) the object's mass and weight will be less on the Moon.

Question 8

A single constant 10-pound force F₁ acts on a body, causing it to accelerate. Then, while F₁ continues to act, a second constant force F₂ is applied to the body, which comes to a momentary stop. The magnitude of F₂ is

A) zero.
B) a bit less than 10 pounds.
C) exactly 10 pounds.
D) larger than 10 pounds.
E) There is not enough information to tell.

Question 9

A car rounds a curve while maintaining constant speed. The correct statement is:

A) The acceleration of the car is zero.
B) No net force acts on the car.
C) The velocity of the car is zero.
D) The velocity of the car is constant.
E) A net force acts upon the car.

Question 10

The force that accelerates a car on a level road is exerted by the

A) road on the tires.
B) gears on the axle .
C) tires on the road.
D) engine on the gears.

Question 11

The starship Enterprise locks onto an alien ship (whose mass is much greater than the Enterprise's mass) with its tractor beam (think of this as a futuristic rope) and starts to pull the alien ship toward it. Neither ship has its propulsion engines running. Which ship has greater acceleration towards the other?

A) The Enterprise
B) The alien ship
C) They both move with equal acceleration.
D) Neither ship can move because there is no friction in outer space.

Question 12

A block of mass 2.5 kg is acted upon by a single force, producing an acceleration of 2.0 m/s². The force has a value of

A) 5.0 N.
B) 10 N.
C) 2.5 N.
D) 0.5 N.

Question 13

All except one of the following require the application of a net force. Which one is the exception?

A) Changing an object from a state of rest to a state of motion
B) Changing an object's speed without changing its direction of motion
C) Maintaining an object in motion at a constant velocity
D) Maintaining an object in uniform circular motion
E) Changing an object's direction of motion without changing its speed

Question 14

Suppose one's hand exerts a force of 12 N upward on a book weighing 10 N. The reaction to the force of the hand on the book is a force of

A) 10 N exerted by the Earth on the book.
B) 10 N exerted by the book on the Earth.
C) 12 N exerted by the book on the hand.
D) 10 N exerted by the book on the hand.
E) 2 N exerted by the book on the hand.

Question 15

An elevator is being lifted upward at a constant speed by a steel cable. All frictional forces are neglected. In this situation, forces on the elevator are such that

A) the upward force by the cable is smaller than the downward force of gravity.
B) the upward force by the cable is equal to the downward force of gravity.
C) the upward force by the cable is greater than the downward force of gravity.
D) None of these. (The elevator goes up because the cable is being shortened, not because an upward force is exerted on the elevator by the cable.)

Question 16

A crate is acted upon by a net force of 100 N. An acceleration of 4.0 m/s² results. The weight of the crate is

A) 25 lb.
B) 25 N.
C) 25 kg.
D) 245 N.
E) 245 lb.

Question 17

The frictional force, due to air resistance, acting on an object is always

A) greater than the net force.
B) in the direction of the object's motion.
C) in the opposite direction to the object's motion.
D) in the upward direction.
E) smaller than object's weight.

Question 18

Two blocks of different mass are connected by a string. The system is accelerated across a smooth horizontal surface by a force supplied by a rubber band connected to the less massive block. The tension in the connecting string will be

A) greater than the force pulling the leading block.
B) the same as the force pulling the leading block.
C) less than the force pulling the leading block.
D) zero.

Question 19

Two pieces of kryptonite, #1 and #2, have identical masses, but the net force applied to #1 is 400 N and to #2 is 20 N. The acceleration

A) of #1 is larger.
B) of each piece of kryptonite is the same.
C) of #2 is larger.
D) depends on the weight of each piece of kryptonite.

Question 20

A block, moving on a frictionless horizontal surface on Earth, requires a force if it is to be stopped. Now suppose that the same block, moving with the same speed on a frictionless horizontal surface on the Moon, where gravity is less, is to be stopped in the same time. We can say that, compared to the Earth,

A) less force is required to stop the block on the Moon.
B) the force required would be the same.
C) greater force is required to stop the block on the Moon.
D) the block could not be stopped.

Question 21

Your mass is 50 kg. Suppose you are standing on a scale in an elevator that starts moving up and increases its speed at the rate of 3 m/s every second. What would be the reading on the scale?

A) 740 N
B) 640 N
C) 340 N
D) 150 N
E) 0 N

Question 22

A child, whose weight is 150 newtons, lifts a pumpkin from the ground with a force of 50 newtons. The force the pumpkin exerts on the child is

A) more than 50 newtons.
B) 50 newtons.
C) greater than zero but less than 50 newtons.
D) zero.

Question 23

An object is acted upon by the three forces shown above. In order to move the object upward,

A) any upward force can be applied.
B) an upward force of at least 5 N must be applied.
C) an upward force of at least 25 N must be applied.
D) an upward force of at least 30 N must be applied.
E) an upward force of at least 55 N must be applied.

Question 24

A parachutist jumping from an airplane reaches a terminal velocity when the force of air resistance is 980 N. The mass of the parachutist is

A) 220 lb.
B) 980 lb.
C) 980 kg.
D) 100 lb.
E) 100 kg.

Question 25

An elevator of mass 500 kg is caused to accelerate upward at 3.0 m/s² by a force in the cable. What is the force exerted by the cable?

A) 1,500 N
B) 4,900 N
C) 6,400 N
D) 2,900 N
E) zero

Question 26

Your weight is 120 lb. Suppose you are standing on a scale in an elevator moving up with a constant speed of 4 m/s. What would be the reading on the scale?

A) 480 lb
B) 120 lb
C) 70 lb
D) 30 lb
E) 0.

Question 27

A dog weighs 200 N. What is his approximate weight in pounds (lb)? (1 lb = 4.45 N)

A) 200 lb
B) 91 lb
C) 32 lb
D) 45 lb
E) 20 lb

Question 28

Three forces act on the object in the sketch. In what direction will the object move?

A) Upward
B) To the left
C) To the left and up
D) To the right
E) To the right and up

Question 29

A certain force causes a 50 kg person to accelerate at 1.0 m/s². The same force applied to a 75-kg person would cause

A) a greater acceleration.
B) the same acceleration.
C) a smaller acceleration.

Question 30

Refer to the set of snapshots Q, J, Y, and L. Which snapshot depicts the forces just after the parachute has fully opened?

A) snapshot Q
B) snapshot J
C) snapshot Y
D) snapshot L

Question 31

Your mass is 50 kg. Suppose you are standing on a scale in an elevator that is approaching a top floor and decreasing its speed at the rate of 3 m/s every second. What would be the reading on the scale?

A) 740 N
B) 640 N
C) 340 N
D) 150 N
E) 0 N

Question 32

Consider two blocks, one made of wood and the other of lead. They have the same dimensions but the lead is much more massive. If they are dropped and fall long enough to reach terminal velocity, which block experiences a larger force from air resistance?

A) The lead block
B) The wood block
C) The force on each is equal.
D) It isn't important because air resistance can be ignored.

Question 33

In the diagram below, a force acting on a block is shown by the arrow labeled F. The mass of the block is known, as is the size of the force, but the observed acceleration is larger than F/m and so another force must act on the block. In which direction (A, B, C, or D) is this force?

A) A
B) B
C) C
D) D

Question 34

The surface gravity of Mars is 3.7 m/s². If a person with mass of 100 kg were parachuting on Mars, what would be the force exerted by air resistance at terminal velocity?

A) 980 N
B) 490 N
C) 370 N
D) 100 N

Question 35

The force exerted on a body by moving air is proportional to the projected area of the body. Which falling body will have the larger terminal velocity, a flying squirrel with its wing membranes extended or a grey squirrel with the same mass?

A) The flying squirrel.
B) The grey squirrel.
C) Both will have same terminal velocity.

Question 36

A shiny, spherical, metal alien jumps out of a perfectly good airplane and skydives for a few seconds. Its photographic friend snaps photos of the sphere with a special camera that also captures the forces on the object. This diagram shows a few of the snapshots, but they are out of order. Place them in order, from the instant it jumps out of the plane and begins free-fall until the time it attains terminal velocity. Assume that the parachute has not deployed yet. If any of the diagrams depict a situation not physically possible, omit it from the ordering.

A) L, Y, J, Q
B) J, Y, L, J
C) L, Q, J
D) Q, Y
E) L, J, Q

Question 37

A father and his young daughter are on very clean ice, so there is very little friction (the father has more mass than the daughter). The father pushes his daughter forward and she slides away at a speed of 3 m/s. The father's velocity is

A) smaller than 3 m/s in the opposite direction as his daughter.
B) zero.
C) smaller than 3 m/s in the same direction as his daughter.
D) 3 m/s in the same direction as his daughter.
E) 3 m/s in the opposite direction as his daughter.

Question 38

When a net horizontal force of 250 N acts on a 50-kg cart that is free to roll on a level surface,

A) the cart accelerates at 9.8 m/s².
B) the cart accelerates at 5 m/s².
C) the cart accelerates at 12500 m/s².
D) the cart accelerates at 0.20 m/s².
E) the cart does not accelerate because it pushes back on the person with a force of 250 N.

Question 39

You stand on a scale to measure your weight. The reaction to the force the Earth exerts on you is

A) the force the scale exerts on you.
B) the force the Earth exerts on the scale.
C) the force you exert on the scale.
D) the force the scale exerts on the Earth.
E) the force you exert on the Earth.

Question 40

The acceleration due to gravity is smaller on Mars than the Earth, so the Mars rovers that explore the surface are lighter on Mars than they are on Earth. If the rovers roll across a flat plain, then the force required to accelerate the rovers is

A) less than would be required on Earth.
B) the same as would be required on Earth.
C) more than would be required on Earth.

Question 41

The amount of inertia a body has can be measured by finding its ___________.

Question 42

A light body sliding on a smooth horizontal surface collides with a heavy body. During the instant of contact the force exerted by the light body on the heavy body is ___________ (equal to, greater than, less than) the force exerted by the heavy body on the light body.

Question 43

The force of the floor pushing up on you to counter your weight is an example of a ________ force.

Question 44

A physics professor places a soda pop can on the table and asks a student to identify the forces acting upon the can and the directions of each force. The two forces acting on the soda pop can are

A) the weight force downward and normal force from the table downward.
B) the weight force downward and normal force from the table upward.
C) the weight force upward and normal force from the table downward.
D) the weight force upward and normal force from the table upward.

Question 45

When an object is at rest, it might have several forces acting on it. However,

A) the forces are all in the same direction.
B) there can only be one force opposite gravity, since weight depends on mass.
C) the forces balance out to net force of zero.
D) dynamic equilibrium can never be achieved except in the total absence of all forces.

Question 46

A blob of green cheese at the Cheese Institute on the Earth has a mass of 8.1 kg. The same cheese blob in outer space will have a mass of ____________ kg.

Question 47

A body of mass 1 kg is pushed across a horizontal table by a force of 1 N. The observed acceleration is 0.7 m/s²_. The force of friction opposing the motion is _______________ N.

Question 48

The net force acting on a body gives the direction of the ________________ of the body.

Question 49

A light body and a heavy body are both given identical accelerations. The body acted upon by the larger force is the ________________ body.

Question 50

In the trajectory of a thrown object, like a baseball, the weight force is always downward. However, the force of air resistance is always

A) upward.
B) horizontal.
C) tangent to the trajectory and in the direction opposite the velocity.
D) perpendicular to the trajectory.
Fill in the Blank Questions

Question 51

A ball hangs at rest from a string attached to the ceiling. The string pulls up on the ball with a force equal to its weight. The reaction to the upward force of the string on the ball is a ___________ (direction) force exerted by the __________ on the _______________.

Question 52

Newton's Law states that no force is required to keep a moving object in motion. Why, then, do you have to pedal continuously to ride a bicycle along a flat road? ____________________________ force