A man weighing 60 kg jumped onto the shore from a stationary boat on the water at a speed of 4 m / s.

A man weighing 60 kg jumped onto the shore from a stationary boat on the water at a speed of 4 m / s. At what speed will the boat move through the water after a person has jumped, if the weight of the boat is 40 kg?

Let’s solve the problem using the law of conservation of momentum:
m1 * v1 + m2 * v2 = m1 * u1 + m2 * u2
v1 = v2 = 0 – because the boat and the person in it were stationary before the jump
The impulse of the boat and the person is oppositely directed, therefore:
0 = m1 * u1-m2 * u2
m1 * u1 = m2 * u2
60 * 4 = 40 * u2
u2 = 240/40
u2 = 6 m / s – the required boat speed