After jumping from a boat weighing 100 kg, a boy weighing 50 kg acquired a horizontal

After jumping from a boat weighing 100 kg, a boy weighing 50 kg acquired a horizontal speed of 10 m / s. How fast will the boat gain?

ml = 100 kg.

mm = 50 kg.

Vm “= 10 m / s.

Vl “-?

Rm + Rl = Rm “+ Rl” – the law of conservation of momentum for a closed boy-boat system.

ml * Vl + mm * Vm = ml * Vl “+ mm * Vm”.

Since before the jump the boat with the boy was at rest, then Vl = Vm = 0 m / s.

0 = ml * Vl “+ mm * Vm”.

ml * Vl “= – mm * Vm”.

Vl “= – mm * Vm” / ml.

Vl “= – 50 kg * 10 m / s / 100 kg = – 5 m / s.

The “-” sign indicates that after the jump, the boat began to move in the opposite direction of the boy’s jump.

Answer: after the jump, the boat began to move in the opposite direction of the boy’s jump at a speed Vl “= 5 m / s.