Deck 4: Force and Motion

Question 1

Explain what is meant by a net or unbalanced force.

Answer 1

An unbalanced, or nonzero, net force always produces an acceleration. In some instances, an applied unbalanced force may also deform an object, that is, change its size and /or shape. A deformation involves a change in motion for some part of an object; hence, there is an acceleration.

Question 2

State Newton's 1st law in your own words.

Answer 2

In the absence of an unbalanced applied force, a body at rest remains at rest, and a body already in motion remains in motion with a constant velocity (constant speed and direction).

Question 3

State Newton's 2nd law in your own words.

Answer 3

The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. The direction of the acceleration is in the direction of the applied net force.

Question 4

The MKS unit of force is a ________, the CGS force unit is a ________, and the English unit for force is a ________.

Question 5

A 170. pound halfback is tackled by a 245. pound guard. Each, of course, exerts a force on the other. Which of the players exerts the LARGER force on the other?

Question 6

State Newton's 3rd law in your own words.

Question 7

We usually think of friction "opposing motion". Explain how friction assists the motion of a car.

Question 8

Your mass on the moon will be about one-sixth of your mass on Earth.

Question 9

The moon pulls on the Earth with one-sixth of the force of the Earth exerts on the moon.

Question 10

The kinetic coefficient of friction is usually larger than the static coefficient of friction.

Question 11

A book can slide down a frictionless hill at constant velocity.

Question 12

Galileo's Law of Inertia is the same as

A) Newton's First Law.
B) Newton's Law of Universal Gravitation.
C) Kepler's Law.
D) Newton's Second Law.
E) Newton's Third Law.

Question 13

Suppose several forces are acting upon a mass m. The in 11eea3d1_0523_35d0_97f4_25e760fe0416_TB9720_11 = m refers to

A) any particular one of the forces.
B) the arithmetic sum of all the forces.
C) the force of friction acting upon the mass.
D) the arithmetic mean of all the forces.
E) the vector sum of all the forces.

Question 14

You are standing in a moving bus, and you suddenly fall backward. You can imply from this that the bus's

A) speed remained the same, but it's turning to the right.
B) velocity decreased.
C) the bus stopped.
D) speed remained the same, but it's turning to the left.
E) velocity increased.

Question 15

A 4-kg mass and a 10-kg mass are acted on by the same constant net force during the same amount of time. Both masses are at rest before the force is applied. The 10-kg mass moves a distance X₁ and the 4-kg mass moves a distance X₂ as a result. Which one of the following statements is true?

A) The ratio X₁/X₂ is equal to 5/2.
B) The ratio X₁/X₂ is equal to (5/2)².
C) The ratio X₁/X₂ is equal to (2/5)².
D) The ratio X₁/X₂ is equal to 2/5.
E) X₁ is equal to X₂.

Question 16

If you push a 4-kg mass with the same force that you push a 10-kg mass from rest, then

A) the 10-kg mass accelerates 4 times faster than the 4-kg mass.
B) the 4-kg mass accelerates 2.5 times faster than the 10-kg mass.
C) the 4-kg mass accelerates 4 times faster than the 10-kg mass.
D) both masses accelerate at the same rate.
E) the 10-kg mass accelerates 2.5 times faster than the 4-kg mass.

Question 17

Who has a greater weight-to-mass ratio, a person weighing 100 lb or a person weighing 150 lb?

A) neither; their ratios are the same
B) the person weighing 100 lb
C) the person weighing 150 lb
D) The question can't be answered; not enough information is given

Question 18

If you blow up a balloon, and then release it, the balloon will fly away as the air rushes out. This is an illustration of

A) Galileo's Law of Inertia.
B) Newton's Second Law.
C) Newton's Third Law.
D) Newton's Law of Universal Gravitation.
E) Newton's First Law.

Question 19

When you sit on a chair, the reaction to your weight is

A) zero if in equilibrium.
B) the Earth being pulled up.
C) the floor pushing up on the chair.
D) the chair pushing on you.
E) your push down on the chair.

Question 20

A child's toy is suspended from the ceiling by means of a string. The Earth pulls downward on the toy with its weight force of 8 N. If this is the "action force," what is the "reaction force"?

A) the string pulling downward on the ceiling with an 8-N force
B) the toy pushing downward on the Earth with an 8-N force
C) the ceiling pulling upward on the string with an 8-N force
D) the toy pulling upward on the Earth with an 8-N force
E) the string pulling upward on the toy with an 8-N force

Question 21

Batter up! Your bat hits the ball pitched to you with a 1500-N instantaneous force. The ball hits the bat with an instantaneous force, whose magnitude is

A) somewhat less than 1500 N.
B) somewhat greater than 1500 N.
C) essentially zero.
D) exactly equal to 1500 N.

Question 22

If you exert a force F on an object, the force which the object exerts on you will

A) depend on the relative masses of you and the object.
B) depend upon your direction of motion.
C) depend on whether or not the object is moving.
D) depend on whether or not you are moving.
E) be F in all cases.

Question 23

An arrow is shot straight up. At the top of its path, the net force acting on it is

A) equal to its weight.
B) instantaneously equal to zero.
C) greater than its weight.
D) horizontal.
E) greater than zero, but less than its weight.

Question 24

See Figure 4.1. If two identical masses are attached by a light cord passing over a massless, frictionless pulley of an Atwood's machine, but at different heights, and then released, then

A) the lower mass will go down.
B) the motion will depend on the amount of the masses.
C) the higher mass will go down.
D) the masses will not move.

Question 25

A 16-kg fish is weighed with two spring scales, each of negligible weight, as shown in Figure 4-2.

What will be the readings on the scales?

A) Each scale will read 8 kg.
B) The sum of the two readings will be 32 kg.
C) The top scale will read 16 kg, and the bottom scale will read zero.
D) The bottom scale will read 16 kg, and the top scale will read zero.
E) Each scale will show a reading greater than zero and less than 16 kg, but the sum of the two readings will be 16 kg.

Question 26

Two identical masses are attached by a light string that passes over a small pulley, as shown in Figure 4-3.

The table and the pulley are frictionless. The masses are moving

A) with an acceleration greater than g.
B) with an acceleration less than g.
C) with an acceleration equal to g.
D) at constant speed.

Question 27

Planning to elope with her boyfriend, Janice slides down a rope from her fourth story window. As she slides down the rope, she tightens harder on the rope which of course increases the tension in the rope. When the upward tension in the rope equals Janice's weight

A) Janice will speed up.
B) Janice will continue down at constant speed.
C) the rope will break.
D) Janice will slow down.
E) Janice will stop moving down the rope.

Question 28

Two toy cars (16 kg and 2 kg) are released simultaneously on an inclined plane that makes an angle of 30° with the horizontal. Which statement best describes their acceleration after being released?

A) The 16-kg car accelerates 8 times faster than the 2-kg car.
B) Both cars accelerate at a rate of g sin(30°).
C) Both cars accelerate at a rate of 0.866 g.
D) The 2-kg car accelerates 8 times faster than the 16-kg car.
E) Both cars accelerate at a rate of 8?g.

Question 29

You fall, while skiing, and one ski (of weight W) loosens and slides down an icy slope (assume no friction), which makes an angle ? with the horizontal. The force that pushes it down along the hill is

A) W cos $\theta$ .
B) W sin $\theta$ .
C) W.
D) zero; it moves with constant velocity.
E) W tan $\theta$ .

Question 30

Two cardboard boxes full of books are in contact with each other on a table, as shown in Figure 4-4. Box H has twice the mass of box G.

If you push on box G with a horizontal force F, then box H will experience a net force of

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

Question 31

A decoration, of mass M, is suspended by a string from the ceiling inside an elevator. The elevator is traveling UPWARD with a constant speed. The tension in the string is

A) less than Mg.
B) equal to Mg.
C) greater than Mg.
D) impossible to tell without knowing the speed.
E) impossible to tell without knowing the decoration mass.

Question 32

To push a piece of heavy furniture across the carpet usually takes more force to get it moving than it takes to keep is moving. This is because

A) of Newton's first law.
B) of Newton's third law.
C) the static coefficient of friction is larger than the kinetic coefficient.
D) the kinetic coefficient of friction is larger than the static coefficient.
E) of Newton's second law.

Question 33

A toolbox, of mass M, is resting on a flat board, as shown in Figure 4-5. One end of the board is lifted up until the toolbox just starts to slide.

The angle $\theta$ that the board makes with the horizontal, for this to occur, depends on the

A) coefficient of kinetic friction, _k.
B) coefficient of static friction, _s.
C) acceleration of gravity, g.
D) mass, M.
E) all of the above quantities.

Question 34

An object is dropped from a helicopter. When it reaches terminal velocity

A) the acceleration finally reaches g.
B) the acceleration of gravity, g, becomes 0.
C) gravity no longer acts upon it.
D) the total force is zero.
E) all of the upward forces add up to zero.

Question 35

A brick and a feather fall to the Earth at their respective terminal velocities. Which object experiences the greater force of air friction?

A) Neither, both experience the same amount of air friction force.
B) the feather
C) the brick

Question 36

What is the weight of a 14.0 kg pumpkin in Newtons?

Question 37

A load of steel of mass 6000 kg rests on the flatbed of a truck. It is held in place by metal brackets that can exert a maximum horizontal force of 8000 N. When the truck is traveling 20.0 m/s, what is the minimum stopping distance if the load is not to slide forward into the cab?

Question 38

A sports car of mass 1000 kg can accelerate from rest to 72. km/h in 6.6 s. What would the average force of the car's engine be?

Question 39

A 3300. kg auto tows a 4500. kg horse trailer. If the engine causes the ground to push the car forward with 8.58 kN:
(a) What is the acceleration of the horse trailer?
(b) What is the forward force on the trailer?
(c) With how much force does the trailer pull back on the car?

Question 40

Michael and Misty are standing motionless together on the ice at the center of a very slippery frozen pond. Michael (mass 75. kg) pushes Misty ( 46. kg), giving her an acceleration of 1.8 m/ s2 for 0.17 s while they were in contact.
(a) What is Michael's acceleration?
(b) Who exerts the greater force on the other?
(c) What is Michael's speed relative to Misty?

Question 41

A rope, tied between a motor and a crate, can pull the crate up a hill of ice (assume no friction) Figure 4-6

The free-body diagram of the crate should contain how many force(s)? Identify them.

Question 42

Consider the Atwood machine in Figure 4-7.
m₁= 33.0kg and m₂= 11.0kg, and the pulley mass is negligible.
Figure 4-7

(a) Determine the acceleration.
(b) What is the tension in the connecting string?

Question 43

A sled of mass 10. kg slides down a flat hill that makes an angle of 10.° with the horizontal. If friction is negligible, what is the resultant force on the sled?

Question 44

Three blocks are pulled by a force f of 16.5 Newtons along a frictionless surface, as shown in Figure 4-8.

What is the acceleration of the system and the tension in the string between m₂ and m₃? (m₁= 3.3 kg, m₂= 1.1 kg, and = 2.2 kg)

Question 45

A 2.0 kg mass and a 5.0 kg mass are hung on opposite sides of an Atwood's machine, and released.
(a) What is the tension in the string?
(b) How much time is required to fall 60 cm from rest?

Question 46

A 10. kg blocks rests on a table (on Earth) Figure 4-9

If someone pushes down on the block with a 48. Newton force, what is the maximum horizontal pull (P) that will not move the block?

Question 47

During the investigation of a traffic accident, police find skid marks 90 m long. They determine the coefficient of friction between the car's tires and the roadway to be 0.50 for the prevailing conditions. Estimate the speed of the car when the brakes were applied.

Question 48

A bulldozer drags a log weighing 500. N along a rough surface. The cable attached to the log makes an angle of 30.° with the ground. The coefficient of static friction between the log and the ground is 0.50. What minimum tension is required in the cable in order for the log to begin to move?

Question 49

A flatbed truck carries a load of steel. Only friction keeps the steel from sliding on the bed of the truck. The driver finds that the minimum distance in which he can stop from a speed of 20.0 mi/h without having the steel slide forward into the truck cab is 20.0 m. What would his minimum stopping distance be when going down a 10.0° incline?

Question 50

An automobile initially moving 72. km/hr jams the brakes and skids to a stop in a distance of 24. meters on a dry pavement but stops in 81.6 m for a wet pavement (the auto weighs 2211.lbs; neglect reaction delay)
(a) What is the coefficient of friction for dry weather?
(b) What is the coefficient in wet weather conditions?
(c) Is this the STATIC or the KINETIC coefficient?

Question 51

Stacy (S) and David (D) are having a tug-of-war by pulling on opposite ends of a 5.0 kg rope. Stacy pulls with a 15. N force. What is David's force if the rope accelerates toward Stacy at 2.0 m/ s²?

A) 15 N
B) 3 N
C) 50 N
D) 5 N
E) 25 N

Question 52

If a force accelerates 4.5 kg at 40.m/ s², that same force would accelerate 18. kg by how much?

A) 0.18 km/ s²
B) 10. m/ s²
C) 0.16 km/ s²
D) 40. m/ s²
E) 32. ft/ s²

Question 53

An antitank weapon fires a 3.0 kg rocket which acquires a speed of 50. m/s after traveling 90. cm down a launching tube. Assuming the rocket was accelerated uniformly, what force acted on it?

A) 5.8 kN
B) 3.6 kN
C) 2.8 kN
D) 2.0 kN
E) 4.2 kN

Question 54

A 1300. N gondola car, at a ski lift, is temporarily suspended at the halfway point, causing the wire to sag by 37.0° below the horizontal, as shown in Figure 4-10.

The tension in the cable is

A) 4.32 × 10³ N
B) 1.63 × 10³ N
C) 2.16 × 10³ N
D) 8.14 × 10² N
E) 1.08 × 10² N

Question 55

Use the Figure 4-11 and the information below to answer the following question(s).
A train consists of a caboose (mass = 1000 kg), a car (mass 2000 kg), and an engine car (mass 2000 kg).


-Refer to Figure 4-11. If the train has an acceleration of 5.50 m/s², then the tension force in the coupling between the middle car and the engine car is

A) 16.5 kN.
B) 27.5 kN.
C) 5.50 kN.
D) 11.0 kN.
E) 8.25 kN.

Question 56

Use the Figure 4-11 and the information below to answer the following question(s).
A train consists of a caboose (mass = 1000 kg), a car (mass 2000 kg), and an engine car (mass 2000 kg).


-Refer to Figure 4-11. The wheels of the engine are pushing back with what force?

A) 16.5 kN
B) 5.50 kN
C) 27.5 kN
D) 11.0 kN
E) 550. N

Question 57

Florence, who weighs 120. lbs, stands on a bathroom scale in an elevator. What will the scale read when the elevator is accelerating downward at 2.0 m/ s²?

A) 1.2 × 10² lb
B) 96. lb
C) 1.56 × 10² lb
D) 86. lb
E) 1.4 × 10² lb

Question 58

An elevator weighing 10,000. N is supported by a steel cable. Determine the tension in the cable when the elevator is accelerated upward at 3.0 m/s². (g = 9.8 m/s²)

A) 11. kN
B) 40. kN
C) 13. kN
D) 10. kN
E) 7.0 kN

Question 59

A 42.0 kg block of ice slides down the plane incline 34.0° in Figure 4-12.
Figure 4-12

Assuming friction is negligible, what is the acceleration of the block down the incline?

A) 2.73 m/ s²
B) 9.80 m/ s²
C) 8.12 m/ s²
D) 6.61 m/ s²
E) 5.48 m/ s²

Question 60

Florence, who weighs 120 lb, stands on a bathroom scale in an elevator. What will she see the scale read when the elevator is accelerating upward at 2.0 m/s²?

A) 1.2 × 10² lb
B) 96 lb
C) 1.6 × 10² lb
D) 1.4 × 10² lb
E) 86 lb

Question 61

Consider a 42.0 kg block of ice sliding down the 34.0° plane, as shown in Figure 4-13.

Assuming the kinetic coefficient of friction is 0.060, what is the acceleration of the block down the incline?

A) 6.56 m/s²
B) 2.73 m/s²
C) 5.00 m/s²
D) 9.74 m/s²
E) 8.06 m/s²

Question 62

A horizontal force of 5.0 N accelerates a 4.0 kg mass, from rest, at a rate of
0)50 m/ s² in the positive direction. What friction force acts on the mass?

A) +3.0 N
B) -2.0 N
C) -3.3 N
D) -3.0 N
E) +2.0 N

Question 63

A wooden block slides directly down an inclined plane, at a constant velocity of 6.0 m/s. How large is the coefficient of kinetic friction, ?_k, if the plane makes an angle of 25.° with the horizontal?

A) 1.2
B) 0.37
C) 0.42
D) 0.91
E) 0.47

Question 64

The coefficients of friction for plastic on wood are ?_s = 0.50 and ?_k = 0.40. How much horizontal force would you need to apply to a 3.0-lb plastic calculator to start it moving from rest?

A) 1.2 N
B) 2.7 N
C) 0.50 N
D) 0.15 N
E) 6.7 N