# Balls weighing 5 kg and 1 kg move towards each other at speeds, moduli equal to 5 m / s.

**Balls weighing 5 kg and 1 kg move towards each other at speeds, moduli equal to 5 m / s. After the central elastic impact, the balls move in one direction, and the speed of the first ball is 2 m / s. Determine the speed of the second ball.**

m1 = 5 kg.

m2 = 1 kg.

V1 = 5 m / s.

V2 = 5 m / s.

V1 “= 2 m / s.

V2 “-?

Let’s write the law of conservation of momentum in vector form: m1 * V1 + m2 * V2 = m1 * V 1 “+ m2 * V2″, where m1, m2 are the masses of the balls, V1, V2 are the speed of the first and second balls before impact, V 1 ” , V2 “- the speed of the balls after impacts.

For projections, the law of conservation of momentum will take the form: m1 * V1 – m2 * V2 = m1 * V 1 “+ m2 * V2”.

V2 “= (m1 * V1 – m2 * V2 – m1 * V 1”) / m2.

V2 “= (5 kg * 5 m / s – 1 kg * 5 m / s – 5 kg * 2 m / s) / 1 kg = 10 m / s.

Answer: the speed of the second ball after the impact will become V2 “= 10 m / s.