A boy weighing 40 kg, standing on skates, push off from the coach and began to move at a speed of 2 m / s.

A boy weighing 40 kg, standing on skates, push off from the coach and began to move at a speed of 2 m / s. What is the mass of the trainer if he began to slide at a speed of 0.5 m / s.

Given a boy weighing m = 40 kg, acquired a speed v = 2m / s, the coach’s speed V = 0.5m / s. Determine trainer mass M.

To solve this problem, it is necessary to apply the law of conservation of momentum. When the boy pushed off the coach, he gave him the same impetus that he himself had acquired. We know the boy’s impulse. In the case of the coach, we know his speed.

m * v = M * V.

From this expression we find the mass of the trainer M.

M = (m * v): V = (40kg * 2m / s): 0.5m / s = 160kg.

The mass of the trainer has been found.