A ball with a mass of 100 g, having a speed of 5 m / s, collides with a stationary ball with a mass of 400 g

A ball with a mass of 100 g, having a speed of 5 m / s, collides with a stationary ball with a mass of 400 g, after which the second ball gets a speed of 2 m / s. What is the speed of the first ball after collision? Neglect the loss of energy.

Let’s use the law of conservation of momentum:

m1v1 + m2v2 = m1v1 ‘+ m2v2’;

Is the initial velocity of the second ball v2 equal to 0? hence:

m1v1 = m1v1 ‘+ m2v2’;

v1 ‘= (m1v1 – m2v2’) / m1 = (0.1 * 5 – 0.4 * 2) / 0.1 = – 3 m / s;

The “-” sign means that the body is moving in the opposite direction with respect to the original trajectory.

Answer: v1 ‘= 3 m / s