Question

A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank, with a horizontal velocity of 3 m/s. With what velocity does the boat begin to move backwards ?

Answer 1

The force F₁ exerted by girl is the ‘action’ and the force F₂ exerted by the boat is the ‘reaction’.
Now, momentum of the girl in one direction must be equal to the momentum of the boat in opposite direction.
m₁ × v₁ = m₂ × v₂
⇒ 50 × 3 = 300 × v₂
⇒ v₂ = 0.5
Hence, velocity with which the boat begins to move backwards is 0.5 m/s.