Junior Secondary · Science

Action and reaction: Practice Questions

5 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Action and reaction.

10 questions26 marksFree, no account

Question 1

1 mark

When you press a light switch to turn on a lamp, what is the reaction force to your finger pushing the switch?

Question 2

1 mark

A book rests on a table. Which of the following statements correctly identifies the reaction force to the gravitational force exerted by the Earth on the book?

Question 3

1 mark

Consider a rocket accelerating upwards immediately after launch. If the upward thrust generated by the engine is \(T\) , the downward gravitational pull on the rocket is \(W\) , and the downward air resistance is \(R\) . Which of the following represents the actual action-reaction pair to the force that propels the rocket (the upward thrust \(T\) )?

Question 4

1 mark

When a swimmer performs a stroke, her hands push the water backwards. According to the principle of action and reaction, which force allows her to move forward through the pool?

Question 5

1 mark

According to Newton's Third Law of Motion, when a swimmer pushes water backward with her hands, what is the reaction force?

Question 6

2 marks

According to the principle of action and reaction, if a student pushes a wall with a horizontal force of \(50 \text{ N}\) to the left, what are the magnitude and direction of the reaction force exerted by the wall on the student's hand?

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Question 7

3 marks

A stationary book rests on a table. According to Newton's Third Law, what is the reaction force to the force of the table pushing upwards on the book (the normal force)? Where does this reaction force act?

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Question 8

5 marks

Explain why a rocket engine is able to produce thrust to change its velocity in the vacuum of outer space, where there is no air to push against, using the principle of action and reaction.

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Question 9

4 marks

The principle of action and reaction is often observed in daily life, such as when someone jumps off a small boat.

a) When a person jumps forward from a small boat toward a pier, the boat is observed to move backwards. Explain this observation using the principle of action and reaction.

b) Clearly identify the action force and the reaction force in this specific interaction.

c) If the person pushes off the boat with a force of \( 120 \text{ N} \), what is the magnitude of the force that the boat exerts on the person?

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Question 10

7 marks

A student of mass \(50 \text{ kg}\) stands on a stationary skateboard on a smooth, horizontal floor. He is initially positioned next to a heavy vertical wall. The student then uses his hands to push the wall horizontally with a force of \(80 \text{ N}\).

(a) State the magnitude and direction of the force that the wall exerts on the student. Name the scientific principle that explains this phenomenon.
(b) Identify the specific action and reaction force pair involved in this interaction. Clearly state which force acts on which object.
(c) The student moves backwards as a result of the push. A classmate argues that since the action and reaction forces are equal and opposite, they should cancel each other out, resulting in a net force of zero and no movement. Explain why this argument is scientifically incorrect.
(d) Suppose the student is replaced by a rocket. Explain how the principle of action and reaction allows a rocket to accelerate in the vacuum of space where there is no air to push against.

Write your answer out first, then check it against the worked solution.

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