Question

Concept Questions3rd Law Questions

1. Two people, Person R and Person L, are each standing on ice skates, Both Person R and Person L have a mass of 75 kg. Person
R pushes with a force of -100 N onto Person L, what happens? Explain your answer in terms of Newton's 3rd Law. What
acceleration would each person experience? Show the correct calculation. Drawa sketch to show this along with your answer
and label the action/reaction force pairs.
2. Now imagine what would happen if in the same scenario described above Person R now has a mass of 120 kg and Person L
has a mass of 60 kg. This time Person L pushes with a force of +50 N onto Person R. Drawa brief sketch to show this, and
make sure that you show the person with more mass as being physically larger than the other person. Label the
action/reaction force pairs correctly. Show the correct calculation for the acceleration that each person would experience.
3. In some action movies a zombie or alien is shot by a person wielding a shotgun and is knocked backwards -5 m or more. Why
is this incorrect based on Newton's 3rd Law? Assume the zombie/alien and the shotgun wielding person each have a mass of
88 kg.

Answer 1

In these scenarios, the acceleration experienced by each person can be calculated using Newton's second law. Action movies often ignore Newton's 3rd Law by showing zombies or aliens being knocked backwards when shot.

Step-by-step explanation:

1. According to Newton's 3rd Law, for every action, there is an equal and opposite reaction. In this scenario, when Person R pushes with a force of -100 N onto Person L, Person L will exert an equal and opposite force (+100 N) on Person R. This is the action-reaction force pair. The acceleration each person experiences can be calculated using Newton's second law, F = m * a, where F is the force, m is the mass, and a is the acceleration.

2. Similarly, in the second scenario, Person L pushes with a force of +50 N onto Person R. Person R, with a mass of 120 kg, will experience an acceleration of a = F/m = 50 N / 120 kg = 0.42 m/s^2. Person L, with a mass of 60 kg, will experience an acceleration of a = F/m = 50 N / 60 kg = 0.83 m/s^2.

3. In action movies, when a zombie or alien is shot and knocked backwards by a shotgun, it violates Newton's 3rd Law. According to the law, the force exerted on the zombie or alien by the shotgun is equal and opposite to the force exerted on the shotgun by the zombie or alien, resulting in no net change in momentum. Therefore, the zombie or alien should not be knocked backwards in reality.

Learn more about Newton's 3rd Law