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

Newton's First and Third Laws Answers

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

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A
X: 45 NY: –45 N
B
X: –45 NY: 30 N
C
X: 30 NY: –45 N
D
X: 30 NY: –30 N
2
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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.
3

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
4

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.
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.
7

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.
8

Lien is pushing a box across a table. She used a force of 100 N to get the box moving. Which force did she overcome to get the box moving?

A
the downward force of gravity on the box
B
the upward force of the table on the box
C
the reaction force on the box
D
the push force on the box
9

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.
10

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.

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