AnswersPOP Physics 2627Lesson 2: Newton's First and Third Laws

Lesson 2: Newton's First and Third Laws Answers

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A car is moving east along a straight, level road at a constant velocity. Which forces form an action/reaction force pair?

A
the force of the tires against the road and the force of the road on the tires
B
the weight of the car and the force of the road pushing up on the car
C
the force of the engine on the car and the force due to friction on the car
D
the normal force on the car and the force of the car pulling on Earth
2
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A ball strikes a wall. It exerts a force of 10 N to the left against the wall and bounces off. What force does the wall exert on the ball?

A
10 N to the left
B
10 N to the right
C
more than 10 N to the left
D
more than 10 N to the right
3

Which statements describe an object in motion that has no external force acting on it? Check all that apply.It accelerates and speeds up.It moves at a constant speed.It decelerates and slows down.It changes direction.It moves in the same direction.

A
It accelerates and speeds up.
B
It moves at a constant speed.
C
It decelerates and slows down.
D
It changes direction.
E
It moves in the same direction.
4

John pushes Hector on a plastic toboggan.The free-body diagram is shown.

Question illustration
A
245 N
B
735 N
C
490 N
D
980 N
5

Juan draws a free-body diagram of an object that is in dynamic equilibrium moving to the left.

Question illustration
A
X: 45 NY: –45 N
B
X: –45 NY: 30 N
C
X: 30 NY: –45 N
D
X: 30 NY: –30 N
6

A box is sitting on the floor. The box was then pulled with a force, Ft. The box did not move. The free-body diagram of the box is shown.

Question illustration
A
It is moving up with a net force of 20 N.
B
It is moving to the right with a net force of 10 N.
C
It is in dynamic equilibrium with a net force of 0 N.
D
It is in static equilibrium with a net force of 0 N.
8

Kamala puts on inline skates and stands facing a wall. When she pushes against the wall, she rolls backward.Why does pushing harder make her roll faster?

A
The force of friction between the wheels and the ground decreases.
B
The force of the wall pushing on her increases.
C
The additional force decreases her weight.
D
The extra force causes an increase of the normal force from the ground.
9

Which object is in static equilibrium?

A
a rolling ball that has a net force acting on it
B
a cruising car that has no net force acting on it
C
a book that has no net force acting on it and is sitting on a table
D
a vase that has a net force acting on it and is sitting on a shelf
10

Which situation is contrary to Newton’s first law of motion?

A
An object at rest begins to move when an external force is applied.
B
A moving object has a constant velocity under the influence of balanced forces.
C
An object at rest stays at rest as long as unbalanced forces act on it.
D
A moving object slows down when an external force is applied.
11

Keisha writes that if an object has any external forces acting on it, then the object can be in dynamic equilibrium but not static equilibrium.Which statement best describes Keisha’s error?

A
An object that is not moving is always in static equilibrium.
B
An object that is moving must be in dynamic equilibrium.
C
An object in either state of equilibrium must have no forces acting on it.
D
An object in either state of equilibrium must have no net force acting on it.
12

In deep space, there is very little friction. Once they launch a probe into deep space, where there are no external forces acting on it, scientists shut the probe’s engines off because the scientists want the probe to

A
stop immediately.
B
speed up.
C
slow down.
D
move at constant velocity.

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