Question

A fat person is standing on a light plank floating on a calm lake. The person walks from one end to the other on the plank. His friend sitting on the shore watches him and finds that the person hardly moves any distance because the plank moves backward about the same distance as the person moves on the plank. Explain.

Answer 1

Answer:

By Newton's third law of motion..

Every action has equal and opposite reaction..

as person moves forward to balance the weight plank has to move backwards..

So that I think due to that relative movement his friend notices that person hardly moves..

thank u

Answer 2

There is no external force on this system, at the same position should remain the center of mass of the system. Because of this, the shore friend finds that the fat person is hardly going.

Explanation:

Because the board is thin, its mass is negligible compared to the fat person. The system's combined mass center that includes the fat person and the board can be considered close to the human.

Since there is no external force on this system, at the same position should remain the center of mass of the system. Because of this, the shore friend finds that the fat person is hardly going.