Question

If a man jumps out from a boat , the boat moves back wards . Why?

Answer 1

When a person jumps ,he/she applies force to the ground. Similarly, when the person jumps from a boat ,the force applied on the boat makes it move backwards.

Answer 2

If a man jumps out from a boat then the boat moves backwards because of the application of Newton's third law of motion.

If the man steps out of the boat,  then he exerts pressure on the boat which is the action as well as the boat then applies an equal force on the man and moves backward(reaction) to enable him to move forward.