A boy weighing 30 kg, standing on skates, horizontally throws a stone weighing 1 kg.

A boy weighing 30 kg, standing on skates, horizontally throws a stone weighing 1 kg. The initial speed of the stone is 3 m / s. Determine the boy’s speed after throwing.

Initial data: m1 (boy’s weight) = 30 kg; m2 (mass of the stone thrown by the boy) = 1 kg; V2 (the speed of the stone after the boy’s throw) = 3 m / s; V1.2 (initial speed of the boy, stone) = 0 m / s.

The boy’s speed after throwing a stone can be determined from the law of conservation of momentum: m1 * V1 + m2 * V2 = (m1 + m2) * V1.2 = 0, whence | m1 * V1 | = | m2 * V2 | and V1 = m2 * V2 / m1.

Let’s calculate: V1 = 1 * 3/30 = 0.1 m / s.

Answer: The boy’s speed after throwing a stone will be 0.1 m / s.