Sitting in the boat, the boy throws a tent weighing 10 kg on the shore, giving it a speed of 4 m / s

Sitting in the boat, the boy throws a tent weighing 10 kg on the shore, giving it a speed of 4 m / s in the horizontal direction, what speed and in which direction the boat gets the weight of the boat with the boy equal to 80 kg.

mp = 10 kg.

Vp “= 4 m / s.

mm = 80 kg.

Vm “-?

Since the boy interacts only with the stick, the boy-stick system can be considered closed.

For a closed-loop system, the momentum conservation law is valid: the sum of the impulses of a closed-loop system does not change.

(mm + mp) * V = mp * Vp “+ mm * Vm”.

Since before throwing the stick, the boy and the stick were at rest V = 0 m / s, the law of conservation of momentum will take the form: mp * Vp “+ mm * Vm” = 0.

mp * Vp “= – mm * Vm”.

Vm “= – mp * Vp” / mm.

The “-” sign indicates that the boy with the boat will move in the opposite direction of throwing the stick.

Vm “= 10 kg * 4 m / s / 80 kg = 0.5 m / s.

Answer: after throwing the stick, the boat with the boy will move in the opposite direction with a speed of Vm “= 0.5 m / s.