Download Which of Newton`s Three Laws does the following statement satisfy

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A
Forces with Friction Theory
1. Two students are discussing their physics homework prior to class. They are discussing an
object that is being acted upon by two individual forces (both in a vertical direction); the
F1 = 30N
free-body diagram for the particular object is shown at the right. During the discussion,
Noah suggests to Anna that the object under discussion could be moving. In fact, Noah
suggests that if friction and air resistance could be ignored (because of their negligible size),
the object could be moving. Anna objects, arguing that the object could not have any
motion. Anna claims that the object must be at rest, perhaps on a table or floor. After all,
F2 = 30N
says Anna, an object experiencing a balance of forces will be at rest. Who is correct?
A. Anna
B. Noah C. Neither is correct.
2. While driving down the road, a firefly strikes the windshield of a bus and makes a quite obvious mess in front
of the face of the driver. This is a clear case of Newton's third law of motion. The firefly hit the bus and the bus
hits the firefly. Which of the two forces is greater: the force on the firefly or the force on the bus
a. Force on the firefly
b. Force on the on bus
C. they are equal
D. not enough information
3. Many people are familiar with the fact that a rifle recoils when fired. This recoil is the result of action-reaction
force pairs. A gunpowder explosion creates hot gases that expand outward allowing the rifle to push forward
on the bullet. Consistent with Newton's third law of motion, the bullet pushes backwards upon the rifle. The
acceleration of the recoiling rifle is ...
a. greater than the acceleration of the bullet.
b. smaller than the acceleration of the bullet.
c. the same size as the acceleration of the bullet
4. A car’s performance is tested on various horizontal road surfaces.
The brakes are applied, causing the rubber tires of the car to slide along
the road without rolling. The tires encounter the greatest force of
friction to stop the car on
a. dry concrete
b. dry asphalt b. wet concrete d. wet asphalt
Approximate coefficients of friction
Static
Kinetic
Rubber on concrete (dry)
.85
.68
Rubber on concrete (wet)
. 80
.58
Rubber on asphalt (dry)
. 84
.67
Rubber on asphalt (wet)
.78
.56
5. Three lab partners - Rick , Glen, and Carl – are discussing an incline problem, where a ball (mass of 66.33kg)
is rolling down a hill at a 30 ◦ incline. They are debating the value of the normal force. Glen claims that the normal
force is 642.22 N; Rick claims that the normal force is 100.26 N; and Carl claims that the normal force is 650 N.
Who is correct?
a. Glen
B. Rick C. Carl
D. no one is correct
6. Assume that you weigh 2000 N. If you are falling down through the air at
constant speed, the force of the air against your body is
a. zero
b. more than 0 but less than 2000 N
c. 2000 N
d. more than 2000N e. need more info
7. with reference to question 6, the net force on your body is
a. zero
b. more than 0 but less than 2000 N
c. 2000 N
d. more than 2000N
8. In Newton’s 3rd law, the “action” force does not cancel with the “reaction” force because:
A. the action force is greater than the reaction force.
B. they act on different objects
C. the are in the same direction
D. the forces could have different magnitudes.
9. If the forces acting upon an object are balanced, then the object
a. must not/cannot be moving.
b. must not/cannot be moving with a constant velocity.
c. must not/cannot be accelerating.
d. none of these
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The following 4 questions (10-14) all pertain to figure C (to the
right). Mrs. McGrath skydives from and parachutes from a
stationary helicopter. Various stages of the fall are shown in
positions a through e in the diagram to the right
10. When Mrs. McGrath’s speed is least; her acceleration is
A) least
Figure C
B) most
11. In which position(s) does Mrs. McGrath’s experience her greatest terminal velocity?
A
B
C
D
E
12. If Mrs. McGrath were heavier, her terminal velocity would be
A. greater
B. less
C. the same
13. Which of the following statements is true?
A. Mrs. McGrath reaches terminal velocity at positions C and E and the terminal velocities
are the same
B. Mrs. McGrath reaches terminal velocity at positions A through C and the terminal velocity
is greatest at c.
C. Mrs. McGrath reaches terminal velocity at positions C and E, the terminal velocity is
greatest at E.
D. none of these
14. Up until the point Mrs. McGrath reaches terminal velocity her acceleration
is _____ and her velocity is _______.
a. increasing, increasing
b. decreasing, decreasing
c. increasing, decreasing
d. decreasing, increasing
Questions 15- 19. Mrs McGrath reaches terminal velocity in about ten seconds.
15. Does Mrs McGrath fall a greater distance the first second she is in free fall,
the ninth second she is in free fall or are the distances the same?
a. first second
b. ninth second
c. equal
16. Does she gain more speed during the first second of the fall, ninth second of the fall or
are the gains in speed the same?
a. first second
b. ninth second
c seeds are the same
17. As a she falls faster and faster through the air (before reaching terminal velocity),
does the net force on her increase, decrease or stay the same?
a. increase
b. decrease
c. stays the same
18. As she experiences free fall, does her acceleration increase, decrease or stay the same?
a. increase
b. decrease
c. stays the same
19. Which of the following illustrations would experience the greatest terminal velocity?
a. 78kg
b. 92kg
c. 78kg
d. 92 kg
e. B and c
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20. A crate rests on a horizontal surface and a woman pulls on it with a 10-N force. No matter what the orientation
of the force, the crate does not move. Rank the situations shown (to the below right) according to the magnitude of
the frictional force of the surface on the crate, greatest to least
A. 3,2,1
B. 2, 1, 3 C. 2, 3, 1
D. 1, 3, 2
E. 1,2,3
21. A medical examiner puts a bag of bones on a bathroom scale in an
elevator. The elevator indicates an apparent weight that is greater than
the actual weight of the bag of bones. The elevator must be:
a) moving downward with a constant speed
b) moving downward with a downward acceleration.
c) moving upward with a constant speed.
d) moving upward with an upward acceleration
e) at rest
22. A shopper pushes an empty cart with a force that accelerates the cart at 1.0 m/s 2. An object is placed in the
cart that is equal in mass to the cart and the shopper applies the same force to the cart. The acceleration of the cart
will
a. decrease by half.
b. increase as the square. c. increase by double
e. stay the same
23. In addition to the force of gravity, 3 forces are exerted on a box. The box will accelerate in the direction of
a.
the net force.
b. the weakest force.
c. the gravitation force.
d.
the frictional force.
e. the greatest force
24. A 50 kg astronaut, in space, throws a 10 kg wrench. The wrench begins to moves away from the astronaut with
an acceleration of 3.1m/s2. The astronaut will
a. remain stationary with respect to the wrench
b. move towards the wrench with the same acceleration.
c. move away from the wrench with a lesser acceleration.
d. move towards the wrench with a greater acceleration.
e. move away from the wrench with the same acceleration.
25. Mass differs from weight in that:
a. the mass of an object is always more than its weight
c. all objects have weight but some lack mass
b. mass can be expressed only in the metric system
d. weight is a force and mass is not
26. Which of the following statements describe free-body diagrams?
I. Force diagrams show force vectors as arrows.
II. Forces exerted on the object are represented.
III. Forces exerted by the object are represented.
a. I and II
b. I and III
c. II and III
d. I, II, and III
27 The gravitational force exerted on an object would most likely be represented by which force vector?
a.
b.
c.
d.
e. depends on the position of the object
28. In an action-reaction pair, the
a. action force is exerted first.
b. action force and the reaction force are equal in magnitude and act in the same direction.
c. action force and the reaction force are contact forces only.
d. action force and the reaction force act on two different objects.
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29. A batter strikes a baseball with a bat. Identify an action-reaction pair and describe the forces exerted by each.
a. The batter exerts a force on the bat; the ball exerts a force on the bat.
b. The batter exerts a force on the bat; the bat exerts a force on the batter.
c. The bat exerts a force on the batter; the bat exerts a force on the ball.
d. The ball exerts a force on the bat; the bat exerts a force on the batter.
30. In interactions of action-reaction pairs involving Earth and everyday objects, the effect on Earth’s motion is
often negligible because
a. contact forces do not obey Newton’s third law.
b. Earth has great inertia.
c. everyday objects cannot exert forces on Earth.
d. all of the above
31. The acceleration due to gravity on Planet X is three times that on the Earth. An object with a mass of 5.0-kg on
Earth would have a mass of ______ on Planet X.
A. 0-kg
B. 5-kg
C. 15-kg
D. 45-kg
E. none of these
32. Consider a ball rolling down an inclined plane. The normal force on the ball.
A. is mg.
B. is greater than mg, always.
C. may be greater or less than mg.
D. is less than mg, always
33. A projectile launched at an angle of 45 above the horizon travels through the air. Compared to the projectile’s
theoretical path with no friction, the actual trajectory of the projectile with air friction is
a. lower and shorter
b. lower and longer
c. higher and shorter
d higher and longer
34. A boy pulls a wooden box along a rough horizontal floor at constant speed by means
of a force P as shown. In the diagram f is the magnitude of the force of friction, N is the
magnitude of the normal force, and Fg is the magnitude of the force of gravity. Which of
the following must be true?
A. P = f and N = Fg
B. P = f and N >Fg
C. P >f and N <Fg
D. P >f and N = Fg
35. Why do raindrops fall with constant speed during the later stages of their descent?
A. The gravitational force decreases as they fall.
B. Air resistance balances with the gravitational force.
C. Gravity cannot increase their speed to more than 9.8 m/s2.
D. None of these
36 An empty wooden crate is slid across a warehouse floor. If the crate were filled, what would happen to the
coefficient of kinetic friction between the crate and the floor?
A. increase
B. decrease
C. remain the same
D. cannot determine, need more information
37. An empty wooden crate is slid across a warehouse floor. If the crate were filled, what would happen to the force
of kinetic friction between the crate and the floor?
A. increase
B. decrease
C. remain the same
D. cannot determine, need more information
38. At a certain moment of time, an object has a net force of zero acting on it.
A. The object must be at rest.
B. The object must slow down.
C. The object could be moving with uniform velocity. D. The object must speed up.
39. A box of Cheerios rests on a table, exerting a downward force on the table.
The reaction to this force is:
A. the force of Earth on the box
B. the force of Earth on the table
C. the force of the table on the box
D. the force of the box on Earth
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40. You are walking east at 10m/s. A friend applies a 10N force on your back, pushing you east. At the same time
another friend applies a 10N force on your chest in the opposite direction (west). The two push on you for a total of
10 seconds, what is your speed now? Assume no friction
a. zero
b. more than 0 but less than 10m/s
c. 10m/s
d. more than 10m/s
e. need more info
41. Ms. Boron holds an eraser to the board with a horizontal force as shown in figure E1. What is the direction of
the normal force on the eraser (refer to figure E2)?
A
B
C
D
E. there is no normal force in this problem
D
F
Figure
E1
B
A
C
42. Which of the following situations describes inertia?
a. A stationary object tends to resist being moved.
b. A moving object tends to resist a change in speed.
c. A moving object tends to resist a change in direction.
d. all of the above
Figure
E2