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Chapter 4 Force and Motion
Name__________________________
The Concepts of Force and Net Force
Choose from the following:
(a) Newton
(b) pound
(c) equilibrium
(d) slug
(e) dyne
(f) cm/s​2
(g) dimensionless
(h) mass
(i) N/m
2) An fps unit of force is which of the units shown above?
Answer: (b) pound
Diff: 1
4) An ​SI ​unit of force is which of the units shown above?
Answer: (a) Newton
Diff: l
6) An amount of inertia is quantified by which physical quantity?
Answer: (h) mass
Diff: 1
26) You toss a ball to a friend. When the ball reaches its maximum altitude, its acceleration
A) changes sign.
B) is zero.
C) is constant.
D) is g/2.
Answer: C (9.80m/s​2​ toward the center of the Earth.)
Diff:2
Inertia and Newton's First Law of Motion
1 ) Galileo's Law of Inertia is the same as
A) Newton's First Law,
B) Newton's Third Law.
C) Kepler's Law.
D) Newton's Second Law.
Answer: A
Diff: 1
3) Your mass on the moon will be about one-sixth of your mass on Earth.
Answer: FALSE (mass the same. Weight is different.)
Diff: 1
4) When the rocket engines on the starship NO-PAIN-NO-GAIN are suddenly turned off, while
traveling in empty space, the starship will
A) go faster and faster.
B) slowly slow down, and then stop,
C) stop immediately.
D) move with constant speed.
E) move perpendicular to the velocity,
Answer: D
Diff: 2
6) 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/s​2​?
A) 25 N
B) 5 N
C) 50 N
D) 3 N
E) 15 N
Answer: B
Diff:2
Newton's Second Law of Motion
1) You are standing in a moving bus, and you suddenly fall backward. You can imply from this that
the bus's
A) velocity increased.
B) speed remained the same, but it's turning to the left.
C) velocity decreased.
D) speed remained the same, but it's turning to the right.
Answer: A
Diff:2
3) The same horizontal force is applied to objects of different mass. Which of the above graphs
illustrates the experimental results?
A) graph a
B) graph b
C) graph c
D) graph d
Answer: A
Diff:2
5) If you push a 4-kg mass with the same force that you push a 10-kg mass from rest, then
A) both masses accelerate at the same rate.
B) the 10-kg mass accelerates 2.5 times faster than the 4-kg mass.
C) the 4-kg mass accelerates 2.5 times faster than the 10-kg mass.
​ nswer: C
A
Diff:2
6) 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) impossible to tell without knowing the speed.
B) greater than Mg.
C) less than Mg.
D) equal to Mg.
Answer: D
Diff:2
8) Suppose several forces are acting upon a mass m. The F in F = ma refers to
A) any particular one of the forces.
B) the vector sum of all the forces.
C) the force of friction acting upon the mass.
D) the arithmetic sum of all the forces.
Answer: B
Diff:1
9) An object is dropped from a helicopter. When it reaches terminal velocity
A) the acceleration finally reaches g.
B) gravity no longer acts upon it.
C) all of the upward forces add up to zero.
D) the net force is zero.
E) the acceleration of gravity, g, becomes 0.
Answer: D
Diff:2
10) If a force accelerates 4.5 kg at 40.m/s​2​, that same force would accelerate 18. kg by how much?
A) 0.18 km/s​2
B) 40. m/s​2
C) 10. m/s​2
D) 32. ft/s​2
E) 0.16 km/s​2
Answer: C
Diff: 2
11) What is the weight of a 14.0 kg pumpkin in Newtons?
Answer: 137. Newtons
Diff: 2
14) 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)​
B)​
C)​
D)​
E)​
4.2 kN
​3.6 kN
​2.8kN
​2.0kN
​5.8 kN
​
Answer: A
Diff: 2
15) Which of the following is not a force unit?
A) pound
B) slug foot/s​2
C) dyne
D) kg
Answer: D
Diff: 2
16) The MKS unit of force is a ________ the CGS force unit is a ___________ and the English unit
for force is a ____
Answer: Newton. Dyne, Pound
Diff: 1
Difficult ​17) 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 20.0m/s,
what is the minimum stopping distance if the load is not to slide forward into the cab?
Answer: 150.m
Diff 2
18) A sports car of mass 1000kg can accelerate from rest to 72. km/h (20.0m/s) in 6.6 s. What would
the average force of the car's tires on the pavement be?
Answer: 3.0 x 10​3​ N
Diff: 2
19) An arrow is shot straight up. At the top of its path, the net force acting on it is
A) instantaneously equal to zero.
B) greater than zero, but less than its weight.
C) greater than its weight.
D) equal to its weight.
E) horizontal.
Answer: D (draw the free body diagram)
Diff:2
20) Who has a greater weight-to-mass ratio, a person weighing 100 lb or a person weighing 150 lb?
A) the person weighing 100 lb
B) the question can't be answered; not enough information is given
C) neither; their ratios are the same
D) the person weighing 150 lb
Answer: C
Diff: 2
21) A book can slide down a frictionless hill at constant velocity.
Answer: FALSE (Net force would have to be zero. Draw the free body diagram. With only
normal force and weight, there would be an unbalanced force accelerating the body. Not
possible without friction or some third force (normal, weight))
Diff: 2
Newton's Third Law of Motion
1) When you sit on a chair, the reaction to your weight is
A) zero if in equilibrium.
B) the chair pushing on you.
C) the Earth being pulled up.
D) your push down on the chair.
Answer: C (weight is the Earth pulling on you. The reaction is something you do to the Earth.)
Diff: 2
2) 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?
Answer: (a) 1.10 m/s​2
(b) 4.95 kN
(c) 4.95 kN
Diff: 3
3) The statement by Newton that "for every action there is an opposite but equal reaction" is which of
his laws of motion?
A) gravitation
B) first law
C) third law
D) fourth law
E) second law
Answer: C
Diff: 2
4) 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?
Answer: neither (Newton's 3rd Law)
Diff1
5) How important is Newton's third law? If nature did not obey Newton's 3​rd​ Law, would our application
of Newton's 2​nd​ law be much different?
Answer: When we apply F=ma to any complex system (group of atoms or masses), we can
ignore internal forces because they cancel each other in pairs. If there were not an
"action-reaction" law, it would be enormously more difficult (if not impossible) to analyze
macroscopic systems (imagine needing to know the internal forces on each of the 6 x 10​26
molecules in a kg-mole).
Diff2
6) 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/s​2​ 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?
Answer: (a) 1.1 m/s​2
(b) neither
(c) 0.49 m/s
Diff: 3
7) State Newton's 3rd law in your own words.
Answer: If one thing pushes another, the other pushes back equally (opposite direction); the
"action-reaction law"
Diff: 2
8) 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 ceiling pulling upward on the string with an 8-N force
C) the string pulling upward on the toy with an 8-N force
D) the toy pulling upward on the Earth with an 8-N force
E) the toy pushing downward on the Earth with an 8-N force
Answer: D (Weight is the Earth pulling on the toy. The reaction is the toy doing something
equal to the Earth.)
Diff: 2
9) 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) exactly equal to 1500 N.
C) essentially zero.
D) somewhat greater than 1500N.
Answer: B
Diff:2
10) The moon pulls on the Earth with one-sixth of the force of the Earth exerts on the moon.
Answer: FALSE (Newton’s 3​rd​ law. The Earth and Moon pull with exactly equal forces.)
Diff: 2
11) 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) be F in all cases.
C) depend on whether or not the object is moving.
D) depend on whether or not you are moving.
E) depend upon your direction of motion.
Answer: B
Diff: 2
12) 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) Newton's Second Law.
B) Galileo's Law of Inertia.
C) Newton's Third Law.
D)Newton's First Law.
Answer: C
Diff: 2
More on Newton's Laws: Free-body Diagrams and Translational Equilibrium
1) When you sit on a chair, the resultant force on you
A) is zero.
B) is up,
C) depends on your weight.
D)is down.
E) is horizontal.
Answer: A
Diff:2
2) A rope, tied between a motor and a crate, can pull the crate up a hill of ice (assume no friction) at
constant velocity. The free-body diagram of the crate should contain how many force(s)? Identify
them.
Answer: Three forces: the weight, the rope pull (tension), and the hill normal force.
Diff:2
8) Florence, who weighs 480. N, stands on a bathroom scale in an elevator. What will the scale read
when the elevator is accelerating downward at 2.0 m/s​2​?
A) 3.4 x 10​2​ N
B) 5.6 x 10​2​ N
C) 4.8 x 10​2​ N
D) 3.8 x 10​2​ N
E) 6.2 x 10​2​ N
Answer: D
Diff:2
9) 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/s​2​. (g = 9.8 m/s​2​)
A) 40. kN
B) 10. kN
C) 7.0 kN
D) 13.kN
E) 11.kN
Answer: D (7,000N)
Diff: 2
11) A 160-N fish is weighed with two spring scales, each of negligible weight, as shown here. What
will be the readings on the scales?
A) The bottom scale will read 160 N, and the top scale will read zero.
B) The sum of the two readings will be 320 N.
C) The top scale will read 160 N, and the bottom scale will read zero.
D) Each scale will show a reading greater than zero and less than 160 N, but the sum of
the two readings will be 160 N.
E) Each scale will read 80 N.
Answer: B
Diff: 2
13) 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 brick
C) the feather
Answer: B (at terminal velocity both objects’ air friction = weight. (net vertical force = zero.
Since brick is heavier, the air friction must be greater.)
Diff:2
19) Florence, who weighs 480 N, 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/s​2​?
A) 3.4 x 10​2​ N
B) 5.8 x 10​2​ N
C) 4.8 x 10​2​ N
D) 3.8 x 10​2​ N
E) 6.4 x 10​2​ N
Answer: B
Diff: 2
21) An astronaut is inside a space capsule in orbit around the Earth. She is able to float inside the
capsule because
A) her weight is zero, and her capsule's weight is zero.
B) she and her capsule move with the same constant velocity.
C) her weight is zero, and her capsule is accelerating.
D) she and her capsule move with the same constant acceleration.
Answer: D
Diff:2
4) An average sized apple weighs how many newtons?
A) 2.
B) 0.04
C) 2 x 10​2
D) 40.
E) 0.004
Answer: A
Diff: 1
22) The number of forces acting on a car parked on a hill is ___. Name them.
Answer: Three. Gravity, road on tires uphill, and road on tires perpendicular (normal).
Diff: 3
12) Four students perform an experiment by pulling an object horizontally across a frictionless table.
They repeat the experiment on several other objects of different masses, always applying just enough
force to produce the same acceleration. They each graph the results, individually.
Which student's graph is correct?
A) graph a
B) graph b
C) graph c
D)graph d
Answer: D
Diff: 2
Difficult ​4) Three blocks are pulled by a force f of 16.5 newtons along a frictionless surface. What is
the acceleration of the system and the tension in the string between m​2​ and m​3​? (m​3​= 3.3 kg, m​2​= 1.1
kg, and m​3​= 2.2 kg)
Answer: 2.5 m/s​2​ and 8.3 N
Diff:3