Answer:
In an elastic collision, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. This means that we can use the conservation of momentum to determine the velocity of the right ball after the collision.
The momentum of an object is equal to its mass multiplied by its velocity, so the initial momentum of the left ball is 0.25 kg * 2.0 m/s = 0.5 kgm/s. Since the initial velocity of the right ball is 0, the total initial momentum of the two balls is 0.5 kgm/s.
After the collision, the total momentum of the two balls must still be 0.5 kg*m/s. Since the mass of the two balls is the same, this means that the velocity of the right ball after the collision must be 2.0 m/s, which is the same as the initial velocity of the left ball.
Therefore, the velocity of the right ball after the elastic collision is 2.0 m/s.