Download Modified True/False

Modified True/False
Indicate whether the sentence or statement is true or false. If false, change the identified word or
phrase to make the sentence or statement true.
1. The normal force
force
that acts on an object is always equal in magnitude and opposite in direction to the gravitational
that is acting on it. _________________________
2. Forces of tension always act vertically upward. ______________________________
3. Friction always acts against an object’s motion relative to the contact surface. _________________________
4. Free body diagrams include all the forces acting on the object, not just those directly responsible for the object’s
motion. ______________________________
5. When forces acting on an object are in equilibrium, the object can still be moving. _________________________
6. The same forces act on two objects having different masses. The more massive object will experience the greater
acceleration provided the forces are not “balanced.” ______________________________
7. An object’s weight depends on the strength of the gravitational field it is in. This varies with latitude, altitude, and
locally. ______________________________
8. Newton’s third law states that forces always act in pairs but the two forces of any pair act on different objects.
_________________________
9. When dynamics problems are analyzed, it is best to resolve forces both parallel and frictional to the object’s motion.
______________________________
14. A car accelerates from rest when a traffic light turns green. A cup of coffee that was sitting on the dashboard of the
car falls into the driver’s lap. The driver could rightly argue that the cup’s apparent motion was due to its inertia. It had a
tendency to stay still and the car accelerated from beneath it. _________________________
15. The sum of all the forces acting on a stationary object is the same as that acting on an object in uniform motion.
_________________________
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
16. Which of the following is NOT considered to be one of the “fundamental forces”?
a. gravity
d. weak nuclear
b. friction
e. electromagnetic
c. strong nuclear
17. Which of the following forces is NOT associated with the “electromagnetic force”?
a. friction
d. gravity
b. tension
e. buoyancy
c. air resistance
18. When analyzing dynamics problems, free-body diagrams
a. should always be used
b. are more useful when analyzing horizontal forces than when analyzing vertical forces
c. should include only the forces that are directly responsible for the acceleration
d. should be used only when objects are accelerating
e. only apply to objects in equilibrium
19. The free-body diagram of a wagon being pulled along a horizontal surface is best represented by
a. A
b. B
c. C
d. D
e. E
21.The free-body diagram of a car in a skid with its brakes locked up is best represented by
a. A
d. D
b. B
e. E
c. C
____ 25.
An object is pushed horizontally at a constant velocity. What can correctly be said about the forces
acting on the object?
a. The force(s) acting forward is/are greater than the force(s) acting backward.
b. The sum of all forces has a value directed forward.
c. The sum of all forces is zero.
d. The forces acting on the object can be said to be “unbalanced.”
e. Newton’s second law best summarizes the effect of the forces acting on the object.
____ 26.
Which of the following is NOT an example of “inertia”?
a. A person’s head jerks back as the car he is riding in accelerates forward.
b. A person’s head jerks forward as the car he is riding in suddenly stops.
c. A person is pressed up against the car door as the car turns a corner.
d. A person is largely unaware of a car’s motion when his eyes are closed.
e. All of the above are examples of inertia.
____ 27.
Which of the following situations would produce the greatest acceleration?
a. A 1.0-N force acting west and a 2.0-N force acting east on a 1.0-kg object.
b. A 3.0-N force acting west and a 5.0-N force acting east on a 2.0-kg object.
c. A 8.0-N force acting west and a 5.0-N force acting east on a 3.0-kg object.
d. A 8.0-N force acting west and a 12.0-N force acting east on a 4.0-kg object.
e. A 1.0-N force acting west and a 9.0-N force acting east on a 5.0-kg object.
____ 28.
An elevator moves downward at a constant speed. What is the relationship between the gravitational
force
acting on the elevator and the tension
in the cable?
a.
d.
b.
e.
c.
____ 29.
An elevator accelerates downward. What is the relationship between the gravitational force
the elevator and the tension
a.
b.
acting on
in the cable that supports the elevator?
d.
e.
c.
____ 30.
An elevator is moving upward at a constant velocity. What is the relationship between the gravitational
force
acting on the elevator and the tension
in the cable that supports the elevator?
a.
d.
b.
e.
c.
____ 31.
a.
b.
c.
d.
e.
____ 32.
a.
b.
c.
d.
e.
____ 33.
a.
b.
c.
d.
e.
____ 34.
a.
b.
c.
____ 35.
a.
b.
c.
An object’s “weight”
depends on its mass
depends on the gravitational field strength
is properly measured in “newtons”
is equivalent to the force of gravity acting on the object
all of the above
With respect to Newton’s third law, the action and reaction forces
being equal, imply a “balanced” force situation
act on different objects
are equal provided the object is at rest
are equal provided the object is moving with uniform motion
are equal provided the object is NOT at rest or moving with uniform motion
According to Newton’s third law, when you walk across a floor, the force that propels you forward is
the force applied by your feet on the floor
the force of friction of your feet on the floor
the force of the floor applied against your feet
exerted upward by the floor on your feet (i.e., the normal force)
the force acting on you working against gravity
A 425-g model rocket is accelerated upward at 86 m/s2 by its engine. What is the value of the force
exerted by the engine on the rocket?
41 N [up]
d. 32 N [up]
41 N [down]
e. 32 N [down]
37 N [up]
Which of the following units is equivalent to a newton (N)?
kg·m/s
d. kg·m/s2
g·cm/s
e. kg·cm/s2
2
kg·s /m
_ 38. A 4.0-kg object, A, and a 2.0-kg object, B, are connected with a rope. A force is applied to another rope attached to the
2.0-kg object that pulls both A and B along a horizontal surface. Which of the following statements is true?
a. The force that B exerts on A is greater than the force that A exerts on B.
b. The force that A exerts on B is greater than the force that B exerts on A.
c. The force that B exerts on A is equal to the force that A exerts on B provided that the
system slides with uniform motion.
d. The force that B exerts on A is equal to the force that A exerts on B regardless of the
motion of the system.
e. The sum of the applied force and the force that B exerts on A is equal to the force that A
exerts on B.
_ 39. Two masses, A and B, hang on opposite ends of a rope suspended over a pulley. The mass of A is greater than the mass
of B. If
represents the force of tension exerted by the rope on mass A and
represents the force of tension exerted
by the rope on mass B, then which of the following statements concerning the forces of tension is true?
a.
d.
b.
e.
c.
_ 40. An airplane has three gliders in tow behind it (glider 1 in front of glider 2 which is in front of glider 3). If FT1 represents
the force of the airplane on glider 1, FT2 represents the force of glider 1 on glider 2, and FT3 represents the force of glider
2 on glider 3, then which of the following statements correctly represents the relationships among these three forces?
a.
d.
b.
e.
c.
_ 41. Two masses hang on opposite ends of a rope suspended over a pulley. The pulley is restrained from rotating and the two
forces:
(the force of tension exerted by the rope on mass A) and
(the force of tension exerted by the rope on
mass B) are found to be equal in magnitude. If the pulley becomes free to rotate and the system begins moving, the
relationship between those forces becomes
a.
d.
b.
e.
c.
_ 43. Three masses are suspended vertically as shown in the diagram below. The system is accelerating upward. What is the
relationship among the forces of tension?
a.
d.
b.
e.
c.
_ 45. A 2.0-kg object is pulled horizontally by a force of 6.3 N along the floor where the coefficient of kinetic friction is 0.24.
What is the object’s acceleration?
a. 5.5 m/s2
d. 1.6 m/s2
2
b. 2.0 m/s
e. 0.80 m/s2
c. 2.0 m/s2
_ 50. Imagine that you are travelling in a train and you have a drink sitting on the dining table in front of you. The train
suddenly stops and the drink ends up in your lap. What force acting on the drink is responsible for its sudden motion?
a. the force of the table acting on the drink
b. the force of the track on the wheels
c. the force of the wheels on the track
d. the force of the drink on itself
e. There is no force acting on the drink that is responsible for its motion.
_ 53. A 1.8-kg object is pulled along the floor with a force of 7.0 N acting horizontally. If the object accelerates at 2.4 m/s 2,
how much kinetic friction is acting?
a. 30 N
d. 7.8 N
b. 11 N
e. 2.7 N
c. 8.3 N
_ 54. A 1.4-kg object is pulled horizontally along the floor against 3.2 N of kinetic friction. If the object accelerates at 5.8
m/s2, what is the value of the applied force?
a. 26 N
d. 6.4 N
b. 11 N
e. 4.9 N
c. 10 N
mpletion
mplete each sentence or statement.
Standing on a moving subway car, people are seen to move from side to side slightly as the car rolls along the track. This
movement is best explained by Newton’s ___________________ laws.
58. The force responsible for moving a propeller-driven airplane is the force of the ____________________ acting on the
____________________.
59. In the diagram below, when the system is being pulled to the right, the greatest tension is ____________________ and
the least is ____________________.
60. When the net force acting on an object is nonzero, the object is certain to ____________________.
61.
For two given surfaces in contact with one another, the coefficient of kinetic friction is
generally ____________________ than the corresponding coefficient of static friction.
tching
Match the situations described below with the Newton’s law that best accounts for the motion.
a. Astronauts feel pushed back into their seats during launch.
b. The force an astronaut exerts on his seat is equal in strength and opposite in direction to
the force the seat exerts on the astronaut.
c. The force exerted by the rocket engine overcomes the forces of gravity and air resistance,
resulting in an upward acceleration of the rocket.
_ 69. Newton’s first law
_ 70. Newton’s second law
_ 71. Newton’s third law
rt Answer
72. Why are free-body diagrams considered to be essential first steps in solving dynamics problems?
73. Describe situations where the normal force and the gravitational force acting on an object are equal. Describe situations
where they are not equal.
74. Differentiate between static and kinetic friction.
n what sense could one argue that Newton wasn’t responsible for Newton’s first law?
77.
Newton’s third law talks about forces always acting in pairs with the two forces
of any pair being equal in strength and opposite in direction. Does this imply a
“balanced” force situation and, if so, how is it possible to ever accelerate
anything?
Sketch a graph that shows
(a) the acceleration of an object of a given mass as a function of the net force acting on that object
(b) the acceleration of an object upon which a given net force is acting as a function of that object’s mass
80. A locomotive pulls a series of train cars. Show that the force in each coupling between the cars decreases steadily from
the front of the train to the rear.
81. The graph below shows the relationship between the force applied to an object initially at rest and its acceleration. Why
does the graph not pass through the origin?
99. Two blocks of mass 500.0 g and 200.0 g are suspended vertically as shown in the diagram. The top string is lifted
vertically upward exerting a force of 8.48 N on the 500.0-g block.
(a) At what rate do the blocks rise?
(b) How much tension must the string connecting the two blocks withstand so it does not break when the blocks
accelerate upward?
(c) If the string connecting the two blocks can withstand only 6.0 N, what maximum force can be exerted on the upper
string without the bottom string breaking?
103. Each dog of an eight-dog sled team can pull with a maximum force of 120.0 N. The frictional resistance of the snow on
the 250.0-kg sled is 600.0 N. Show the appropriate free-body diagram in each of the following questions.
(a) What is the maximum acceleration of the sled?
(b) If a second sled of mass 100.0 kg were to be towed behind the larger one with a frictional resistance of 240.0 N
acting on the smaller sled, what maximum acceleration could the dogs supply?
(c) Calculate the tension in the rope connecting the two sleds in (b).
(d) Once the two sleds are up to speed, with what force must each dog pull to keep the sleds moving at a constant speed?
104. Three books rest horizontally on a table as pictured below. What forces does the middle book exert on each of the other
two? Be specific in expressing your answers.
ay
105. Elite athletes are always looking for ways to gain an advantage over their competitors. In recent years, the design of
equipment and uniforms for high-speed sports such as speed skating, skiing, running, and swimming has seen
innovations in this regard. Discuss this topic briefly using physics principles.
106. Some of the recent innovations in automobile safety design include air bags and impact beams. Discuss the principles of
dynamics on which these are based.
107. In the animal kingdom, speed can often be an essential attribute. Provide some examples where streamlining has given
certain species an advantage in this regard.
108. Consider a ride in a high-speed elevator from the ground floor upward and from the top floor down. Describe the
sensations one feels during all parts of the trip and explain them in terms of the physics involved.