Question

Mike is trying to push a truck, but Sam tells him that he won't be able to do so. Sam justifies this by answering that the two opposite and equal forces cancel each other out. Comment on this logic and explain why the truck does not move.​

Answer 1

According to Newton's third law states that when two bodies come into contact, they apply forces to one another that are equal in magnitude and opposite in direction.

Student’s justification:

1. The student’s justification is incorrect since action as well as reaction always apply to different bodies and hence cannot cancel each other.
2. But when two equal and opposite forces act on the same body, they cancel each other.

Truck's movement:

1. A stationary truck has a huge weight and generates greater friction force between its tires and the ground than the force applied.
2. Hence, the truck will only move if a force greater than the friction force is applied to it.

Thus, the truck will not move until a force, which must be greater than frictional force, acts on it.