# Two balls, the masses of which are 30g and 15g, move at the same speed

**Two balls, the masses of which are 30g and 15g, move at the same speed of 3m / s towards each other. With what speeds will they scatter after an absolutely elastic central impact?**

m1 = 30 g = 0.03 kg.

m2 = 15 g = 0.015 kg.

V1 = 3 m / s.

V2 = 3 m / s.

V “-?

Let us write the law of conservation of momentum in vector form for balls: р1 + р2 = р1 “+ р2”, where р1, р2 are the momentum of the first and second balls before impact, р1 “, р2” – momentum of balls after impact.

The momentum of the ball p is the product of the mass of the ball m by its velocity V: p = m * V.

The law of conservation of momentum in vector form will look like: m1 * V1 + m2 * V2 = m1 * V “+ m2 * V”.

Since the balls move towards each other before impact, then m1 * V1 – m2 * V2 = (m1 + m2) * V “.

V “= (m1 * V1 – m2 * V2) / (m1 + m2).

V “= (0.03 kg * 3 m / s – 0.015 kg * 3 m / s) / (0.03 kg + 0.015 kg) = 1 m / s.

Answer: V “= 1 m / s.