Deck 5: Force and Motion I

Question 1

The unit of force called the newton is:

A) 9.8 kg . m/s²
B) 1 kg . m/s²
C) defined by means of Newton's third law
D) 1 kg of mass
E) 1 kg of force

Answer 1

1 kg . m/s²

Question 2

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

Answer 2

of the net force

Question 3

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 orientations 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

Answer 3

I

Question 4

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
E) an undetermined amount

Question 5

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 6

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 7

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 8

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 9

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

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

Question 10

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 11

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 12

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

Question 13

Which of the following quantities is NOT a vector?

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

Question 14

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

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

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 17

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 18

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 19

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 20

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 21

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 22

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 23

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

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

Question 24

A 70-N block and an 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) 6.7 m/s²
E) 9.8 m/s²

Question 25

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 26

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 27

A 1000-kg elevator is rising and its speed is increasing at 3 m/s². The tension in the elevator cable is:

A) 6800 N
B) 1000 N
C) 3000 N
D) 9800 N
E) 12800 N

Question 28

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 29

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 30

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 31

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 32

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 33

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 34

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 35

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 36

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 37

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 38

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 39

An object rests on a horizontal frictionless surface. A 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 40

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) zero
C) 9.8 N, up
D) 9.8 N, down
E) 1.5 N, down

Question 41

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 42

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 43

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 44

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 45

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 46

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 47

A 5-kg block is suspended by a rope from the ceiling of an elevator 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 48

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

A) the action force is greater than the reaction force
B) they are 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 49

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 50

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) zero
E) none of these

Question 51

You stand on a spring scaleon 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 52

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

Question 53

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 54

A car moves horizontally 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 55

Three blocks (A,B,C), each having mass M, are connected by strings as shown. Block C is pulled to the right by a force that causes the entire system to accelerate. Neglecting friction, the net force acting on block B is:

A) zero
B)
C)
D)
E)

Question 56

A block slides down a frictionless plane that makes an angle of 30 $\degree$ with the horizontal. The acceleration of the block (in cm/s²) is:

A) 980
B) 566
C) 849
D) zero
E) 490

Question 57

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 (in newtons) is:

A) cos $\theta$
B) 2/cos $\theta$
C)
D) 1
E) none of these

Question 58

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 59

A man weighing 700 Nb 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 60

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, 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 61

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 62

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 63

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

Question 64

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 65

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) zero
B) 90 N
C) 880 N
D) 450 N
E) 49 N

Question 66

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

Question 67

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) zero
B) 90 N
C) 760 N
D) 880 N
E) 1010 N

Question 68

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