Deck 5: Force and Motion I

Question 1

The block shown moves with constant velocity on a horizontal surface. Two of the forces on it are shown. A frictional force exerted by the surface is the only other horizontal force on the block. The frictional force is:

A) 0 N
B) 2 N, leftward
C) 2 N, rightward
D) slightly more than 2 N, leftward
E) slightly less than 2 N, leftward

Answer 1

B

Question 2

A newton is the force:

A) of gravity on a 1 kg body
B) of gravity on a 1 g body
C) that gives a l g body an acceleration of 1 cm/s²
D) that gives a 1 kg body an acceleration of 1 m/s²
E) that gives a 1 kg body an acceleration of 9.8 m/s²

Answer 2

D

Question 3

A motionless 400-N steel ball is suspended by a light rope from the ceiling. The tension in the rope is:

A) 400 N
B) 800 N
C) 0 N
D) 200 N
E) 560 N

Answer 3

A

Question 4

A circus performer of weight W is walking along a "high wire" as shown. The tension in the wire is:

A) approximately W
B) approximately W/2
C) much less than W
D) much more than W
E) depends on whether he stands on one or two feet

Question 5

The unit of force called the newton is:

A) the force needed to accelerate a mass of 1 kg at a rate of 9.8 m/s²
B) the force needed to accelerate a mass of 1 kg at a rate of 1 m/s²
C) defined by means of Newton's third law
D) 1 kg of mass
E) 1 kg of force

Question 6

When a certain force is applied to the 1-kg standard mass its acceleration is 5.0 m/s². When the same force is applied to another object its acceleration is one-fifth as much. The mass of the object is:

A) 0.2 kg
B) 0.5 kg
C) 1.0 kg
D) 5.0 kg
E) 10 kg

Question 7

Two forces, one with a magnitude of 3 N and the other with a magnitude of 5 N, are applied to an object. For which orientation of the forces shown in the diagrams is the magnitude of the acceleration of the object the least?

A) I
B) II
C) III
D) IV
E) V

Question 8

Which of the following is a correct statement of Newton's first law?

A) An object in motion will continue in motion at a constant speed unless acted on by a net external force.
B) An object at rest will stay at rest unless acted on by a net internal force.
C) An object in motion will continue in motion at a constant velocity unless acted on by a net internal force.
D) An object in motion will continue in motion at a constant velocity unless acted on by a net external force.
E) Everything has inertia.

Question 9

A heavy ball is suspended as shown. A quick jerk on the lower string will break that string but a slow pull on the lower string will break the upper string. The first result occurs because:

A) the force is too small to move the ball
B) action and reaction is operating
C) the ball has inertia
D) air friction holds the ball back
E) the ball has too much energy

Question 10

In SI units a force is numerically equal to the ______, when the force is applied to it.

A) velocity of the standard kilogram
B) speed of the standard kilogram
C) velocity of any object
D) acceleration of the standard kilogram
E) acceleration of any object

Question 11

An example of an inertial reference frame is:

A) any reference frame that is not accelerating
B) a frame attached to a particle on which there are no forces
C) any reference frame that is at rest
D) a reference frame attached to the center of the universe
E) a reference frame attached to the Earth

Question 12

An object moving at constant velocity in an inertial frame must:

A) have a net force on it
B) eventually stop due to gravity
C) not have any force of gravity acting on it
D) have zero net force acting on it
E) have no frictional force acting on it

Question 13

The term "mass" refers to the same physical concept as:

A) weight
B) inertia
C) force
D) acceleration
E) volume

Question 14

A force of 1 N is:

A) 1 kg/s
B) 1kg. m/s
C) 1kg . m/s²
D) 1kg . m²/s
E) 1kg . m²/s²

Question 15

The mass of a body:

A) is slightly different at different places on the Earth
B) is a vector
C) is independent of the acceleration due to gravity
D) is the same for all bodies of the same volume
E) can be measured most accurately on a spring scale

Question 16

Which of the following quantities is NOT a vector?

A) Mass
B) Displacement
C) Weight
D) Acceleration
E) Force

Question 17

The inertia of a body tends to cause the body to:

A) speed up
B) slow down
C) resist any change in its motion
D) fall toward the Earth
E) decelerate due to friction

Question 18

The standard 1-kg mass is attached to a compressed spring and the spring is released. If the mass initially has an acceleration of 5.6 m/s², the force of the spring has a magnitude of:

A) 2.8 N
B) 5.6 N
C) 11.2 N
D) 0 N
E) an undetermined amount

Question 19

Which of the following is true, according to Newton's second law?

A) The acceleration of an object is proportional to its mass and inversely proportional to the net force on it.
B) The acceleration of an object is proportional to the product of its mass and the net force on it.
C) The acceleration of an object is proportional to the net force on it and inversely proportional to its mass.
D) The acceleration of an object is equal to the net force on it.
E) The acceleration of an object depends on all the forces on it, both internal and external.

Question 20

Mass differs from weight in that:

A) all objects have weight but some lack mass
B) weight is a force and mass is not
C) the mass of an object is always more than its weight
D) mass can only be expressed in the metric system
E) there is no difference

Question 21

You are driving your car along the road and hit a patch that is so icy that there is effectively no friction between your tires and the road. Which statement is most accurate?

A) If you hit the brakes, you will eventually stop.
B) If you twist the steering wheel, you can turn into the skid.
C) Nothing you do will have any effect; without any friction, you will continue to move in a straight line at a constant speed, as there is no net external force on you.
D) If you hit the accelerator, you will get out of the icy patch faster.
E) Your car will start to spin.

Question 22

The mass and weight of a body:

A) differ by a factor of 9.8
B) are identical
C) are the same physical quantities expressed in different units
D) are both a direct measure of the inertia of the body
E) have the same ratio as that of any other body placed at that location

Question 23

An object placed on an equal-arm balance requires 12 kg to balance it. When placed on a spring scale, the scale reads 12 kg. Everything (balance, scale, set of weights and object) is now transported to the Moon where free-fall acceleration is one-sixth that on Earth. The new readings of the balance and spring scale (respectively) are:

A) 12 kg, 12 kg
B) 2 kg, 2 kg
C) 12 kg, 2 kg
D) 2 kg, 12 kg
E) 12 kg, 72 kg

Question 24

Acceleration is always in the direction:

A) of the displacement
B) of the initial velocity
C) of the final velocity
D) of the net force
E) opposite to the frictional force

Question 25

A 90-kg man stands in an elevator that has a downward acceleration of 1.4 m/s². The force exerted by him on the floor is about:

A) 0 N
B) 90 N
C) 760 N
D) 880 N
E) 1010 N

Question 26

You stand on a spring scale on the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

A) moves upward with increasing speed
B) moves upward with decreasing speed
C) remains stationary
D) moves downward with increasing speed
E) moves downward at constant speed

Question 27

You stand on a spring scale on the floor of an elevator. Of the following, the scale shows the highest reading when the elevator:

A) moves downward with increasing speed
B) moves downward with decreasing speed
C) remains stationary
D) moves upward with decreasing speed
E) moves upward at constant speed

Question 28

A crate rests on a horizontal surface and a woman pulls on it with a 10-N force. Rank the situations shown below according to the magnitude of the normal force exerted by the surface on the crate, least to greatest.

A) 1, 2, 3
B) 2, 1, 3
C) 2, 3, 1
D) 1, 3, 2
E) 3, 2, 1

Question 29

A box is on a scale. In which of these situations will the scale reading NOT equal the weight of the box?

A) The scale and box are in an airplane flying at constant speed.
B) The scale and box are in an elevator rising at constant speed.
C) The scale and box are in a hot air balloon in level flight.
D) The scale and box are on a steep slope, held in place by friction.
E) The scale and box are on Mars.

Question 30

An object rests on a horizontal frictionless surface. A net horizontal force of magnitude F is applied. This force produces an acceleration:

A) only if F is larger than the weight of the object
B) only while the object suddenly changes from rest to motion
C) always
D) only if the inertia of the object decreases
E) only if F is increasing

Question 31

A constant force of 8.0 N is exerted for 4.0 s on a 16-kg object initially at rest. The change in speed of this object will be:

A) 0.5 m/s
B) 2 m/s
C) 4 m/s
D) 8 m/s
E) 32 m/s

Question 32

A car travels east at constant velocity. The net force on the car is:

A) east
B) west
C) up
D) down
E) zero

Question 33

A man weighing 700 N is in an elevator that is accelerating upward at 4 m/s². The force exerted on him by the elevator floor is:

A) 71 N
B) 290 N
C) 410 N
D) 700 N
E) 990 N

Question 34

Equal forces act on isolated bodies A and B. The mass of B is three times that of A. The magnitude of the acceleration of A is:

A) three times that of B
B) 1/3 that of B
C) the same as B
D) nine times that of B
E) 1/9 that of B

Question 35

A ball with a weight of 1.5 N is thrown at an angle of 30 $\degree$ above the horizontal with an initial speed of 12 m/s. At its highest point, the net force on the ball is:

A) 9.8 N, 30 $\degree$ below horizontal
B) 0 N
C) 9.8 N, up
D) 9.8 N, down
E) 1.5 N, down

Question 36

A 6-kg object is moving south. A net force of 12 N north on it result in the object having an acceleration of:

A) 2 m/s², north
B) 2 m/s², south
C) 6 m/s², north
D) 18 m/s², north
E) 18 m/s², south

Question 37

A heavy steel ball B is suspended by a cord from a block of wood W. The entire system is dropped through the air. Neglecting air resistance, the tension in the cord is:

A) zero
B) the difference in the masses of B and W
C) the difference in the weights of B and W
D) the weight of B
E) none of these

Question 38

A 9000-N automobile is pushed along a level road by four students who apply a total forward force of 500 N. Neglecting friction, the acceleration of the automobile is:

A) 0.055m/s²
B) 0.54 m/s²
C) 1.8 m/s²
D) 9.8 m/s²
E) 18 m/s²

Question 39

A 90-kg man stands in an elevator that is moving up at a constant speed of 5.0 m/s. The force exerted by him on the floor is about:

A) 0 N
B) 90 N
C) 880 N
D) 450 N
E) 49 N

Question 40

When a 25-kg crate is pushed across a frictionless horizontal floor with a force of 200 N, directed 20 $\degree$ below the horizontal, the magnitude of the normal force of the floor on the crate is:

A) 25 N
B) 68 N
C) 180 N
D) 250 N
E) 310 N

Question 41

A massless rope passes over a massless pulley suspended from the ceiling. A 4-kg block is attached to one end and a 5-kg block is attached to the other end. The acceleration of the 5-kg block is:

A) g/4
B) 5g/9
C) 4g/9
D) g/5
E) g/9

Question 42

A 70-N block and a 35-N block are connected by a string as shown. If the pulley is massless and the surface is frictionless, the magnitude of the acceleration of the 35-N block is:

A) 1.6 m/s²
B) 3.3 m/s²
C) 4.9 m/s²
D) 6.5 m/s²
E) 9.8 m/s²

Question 43

Two blocks are connected by a string and pulley as shown. Assuming that the string and pulley are massless, the magnitude of the acceleration of each block is:

A) 0.049 m/s²
B) 0.020 m/s²
C) 0.0098 m/s²
D) 0.54 m/s²
E) 0.98 m/s²

Question 44

A 13-N weight and a 12-N weight are connected by a massless string over a massless, frictionless pulley. The 13-N weight has a downward acceleration with magnitude equal to that of a freely falling body times:

A) 1
B) 1/12
C) 1/13
D) 1/25
E) 13/25

Question 45

A book rests on a table, exerting a downward force on the table. The reaction to this force is:

A) the force of the Earth on the book
B) the force of the table on the book
C) the force of the Earth on the table
D) the force of the book on the Earth
E) the inertia of the book

Question 46

A heavy wooden block is dragged by a force along a rough steel plate, as shown below for two cases. The magnitude of the applied force is the same for both cases. The normal force in (ii), as compared with the normal force in (i) is:

A) the same
B) greater
C) less
D) less for some angles of the incline and greater for others
E) less or greater, depending on the magnitude of the applied force

Question 47

The "reaction" force does not cancel the "action" force because:

A) the action force is greater than the reaction force
B) they act on different bodies
C) they are in the same direction
D) the reaction force exists only after the action force is removed
E) the reaction force is greater than the action force

Question 48

A 25-kg crate is pushed across a frictionless horizontal floor with a force of 20 N, directed 20 $\degree$ below the horizontal. The acceleration of the crate is:

A) 0.27 m/s²
B) 0.75 m/s²
C) 0.80 m/s²
D) 170 m/s²
E) 470 m/s²

Question 49

Two forces are applied to a 5.0-kg crate; one is 6.0 N to the north and the other is 8.0 N to the west. The magnitude of the acceleration of the crate is:

A) 0.50 m/s²
B) 2.0 m/s²
C) 2.8 m/s²
D) 10 m/s²
E) 50 m/s²

Question 50

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The force of book Z on book Y is:

A) 0 N
B) 5 N
C) 9 N
D) 14 N
E) 19 N

Question 51

Two blocks are connected by a massless string that passes over a massless pulley, as shown. In the absence of friction, how does the tension force exerted by the string on the 250 N block compare with the tension force exerted by the string on the 350 N block?

A) The force on the 250 N block is smaller by a factor of 0.71.
B) The force on the 250 N block is larger by a factor of 1.4.
C) The force on the 250 N block is always equal to its weight.
D) The force on the 250 N block is equal to the weight of the 350 N block.
E) The two forces are equal.

Question 52

Three books (X, Y, and Z) rest on a table. The weight of each book is indicated. The net force acting on book Y is:

A) 4 N down
B) 5 N up
C) 9 N down
D) 0 N
E) none of these

Question 53

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the rope is:

A) 14 N, up
B) 14 N, down
C) 35 N, up
D) 35 N, down
E) 49 N, up

Question 54

In general, any surface exerts two forces on objects that are in contact with it. One force is parallel to the surface and the other is perpendicular to the surface. What are these forces called?

A) The parallel force is surface tension and the perpendicular force is friction.
B) The parallel force is the normal force and the perpendicular force is friction.
C) The parallel force is friction and the perpendicular force is surface tension.
D) The parallel force is friction and the perpendicular force is the normal force.
E) The parallel force is static friction and the perpendicular force is kinetic friction.

Question 55

A 5-kg concrete block is lowered with a downward acceleration of 2.8 m/s² by means of a rope. The force of the block on the Earth is:

A) 14 N, up
B) 14 N, down
C) 35 N, up
D) 35 N, down
E) 49 N, up

Question 56

A 5-kg block is suspended by a rope from the ceiling of an elevator that accelerates downward at 3.0 m/s². The tension force of the rope on the block is:

A) 15 N, up
B) 34 N, up
C) 34 N, down
D) 64 N, up
E) 64 N, down

Question 57

A feather and a lead ball are dropped from rest in vacuum on the Moon. The acceleration of the feather is:

A) more than that of the lead ball
B) the same as that of the lead ball
C) less than that of the lead ball
D) 9.8 m/s²
E) zero since it floats in a vacuum

Question 58

A lead block is suspended from your hand by a string. The reaction to the force of gravity on the block is the force exerted by the:

A) string on the block
B) block on the string
C) string on the hand
D) hand on the string
E) block on the Earth

Question 59

Two objects, one having three times the mass of the other, are dropped from the same height in a vacuum. At the end of their fall, their velocities are equal because:

A) anything falling in vacuum has constant velocity
B) all objects reach the same terminal velocity
C) the acceleration of the larger object is three times greater than that of the smaller object
D) the force of gravity is the same for both objects
E) none of the above

Question 60

A 1100-kg elevator is rising and its speed is increasing at 3.0 m/s². The tension in the elevator cable is:

A) 7500 N
B) 1100 N
C) 3300 N
D) 11000 N
E) 14000 N

Question 61

A 1-N pendulum bob is held at an angle $\theta$ from the vertical by a 2-N horizontal force F as shown. The tension in the string supporting the pendulum bob is:

A) 2/N
B) 2 N
C) N
D) 1 N
E) none of these

Question 62

A short 10-g string is used to pull a 50-g toy across a frictionless horizontal surface. If a 3.0 *10^-2 N force is applied horizontally to the free end of the string, the force of the string on the toy, at the other end, is:

A) 0.15 N
B) 6.0 * 10^-3 N
C) 2.5*10^-2 N
D) 3.0 * 10^-2 N
E) 3.5 *10^-2 N

Question 63

A 25-N crate slides down a frictionless incline that is 25 $\degree$ above the horizontal. The magnitude of the normal force of the incline on the crate is:

A) 11 N
B) 23 N
C) 25 N
D) 100 N
E) 220 N

Question 64

A block slides down a frictionless plane that makes an angle of 30 $\degree$ with the horizontal. The acceleration of the block is:

A) 9.80 m/s²
B) 5.66 m/s²
C) 8.49 m/s²
D) 0 m/s²
E) 4.90 m/s²

Question 65

When a 40-N force, parallel to the incline and directed up the incline, is applied to a crate on a frictionless incline that is 30 $\degree$ above the horizontal, the acceleration of the crate is 2.0 m/s², up the incline. The mass of the crate is:

A) 3.8 kg
B) 4.1 kg
C) 5.8 kg
D) 6.2 kg
E) 10 kg

Question 66

A crane operator lowers a 16,000 N steel ball with a downward acceleration of 3 m/s². The tension in the cable is:

A) 4900 N
B) 11,000 N
C) 16,000 N
D) 21,000 N
E) 48,000 N

Question 67

A 32-N force, parallel to the incline, is required to push a certain crate at constant velocity up a frictionless incline that is 30 $\degree$ above the horizontal. The mass of the crate is:

A) 3.3 kg
B) 3.8 kg
C) 5.7 kg
D) 6.5 kg
E) 160 kg

Question 68

A car drives in a straight line on a level road with a constant acceleration of 3 m/s². A ball is suspended by a string from the ceiling of the car; the ball does not swing, being at rest with respect to the car. What angle does the string make with the vertical?

A) 17 $\degree$
B) 35 $\degree$
C) 52 $\degree$
D) 73 $\degree$
E) Cannot be found without knowing the length of the string

Question 69

A sled is on an icy (frictionless) slope that is 30 $\degree$ above the horizontal. When a 40-N force, parallel to the incline and directed up the incline, is applied to the sled, the acceleration of the sled is 2.0 m/s², down the incline. The mass of the sled is:

A) 4.1 kg
B) 6.2 kg
C) 8.1 kg
D) 10 kg
E) 14 kg

Question 70

Two blocks with masses m and M are pushed along a horizontal frictionless surface by a horizontal applied force as shown. The magnitude of the force of either of these blocks on the other is:

A) mF/(m + M)
B) mF/M
C) mF/(M - m)
D) MF/(M + m)
E) MF/m

Question 71

A 25-N crate is held at rest on a frictionless incline by a force that is parallel to the incline. If the incline is 25 $\degree$ above the horizontal the magnitude of the applied force is:

A) 4.1 N
B) 4.6 N
C) 8.9 N
D) 11 N
E) 23 N

Question 72

Two blocks weighing 250 N and 350 N respectively, are connected by a string that passes over a massless pulley as shown. The tension in the string is:

A) 210 N
B) 290 N
C) 410 N
D) 500 N
E) 4900 N

Question 73

A 25-N crate is held at rest on a frictionless incline by a force that is parallel to the incline. If the incline is 25 $\degree$ above the horizontal the magnitude of the normal force of the incline on the crate is:

A) 4.1 N
B) 4.6 N
C) 8.9 N
D) 11 N
E) 23 N