# Two inelastic balls with masses of 6 and 4 kg are moving towards each other with speeds equal to 8 and 3 m / s

**Two inelastic balls with masses of 6 and 4 kg are moving towards each other with speeds equal to 8 and 3 m / s, respectively, directed along one straight line. How fast will the balls move after an absolutely inelastic collision?**

Given:

m1 = 6 (kilogram) is the mass of the first ball;

m2 = 4 (kilogram) – the mass of the second ball;

u1 = 8 meters / second – the speed of the ball m1 before interaction;

u2 = 3 meters / second – the speed of the m2 ball before interaction.

It is required to determine u (meter / second) – with what speed the balls will move after an absolutely inelastic collision.

In a completely inelastic collision, the balls will move together after interacting. Then, let the first ball move in the positive direction of the coordinate system, and the second ball in the negative direction. According to the law of conservation of momentum, we obtain:

m1 * u1 – m2 * u2 = (m1 + m2) * u;

u = (m1 * u1 – m2 * u2) / (m1 + m2);

u = (6 * 8 – 4 * 3) / (6 + 4) = (48 – 12) / 10 = 36/10 = 3.6 meters / second.

Answer: after interaction, the balls will move at a speed of 3.6 m / s.