Four smooth steel balls of equal mass at rest are free to move along a straight line without friction. The first ball is given a velocity of 0.4 𝑚/𝑠. It collides head on with the second elastically, the second one similarly with the third and so on. The velocity of the last ball is

Question: Four smooth steel balls of equal mass at rest are free to move along a straight line without friction. The first ball is given a velocity of 0.4 𝑚/𝑠. It collides head on with the second elastically, the second one similarly with the third and so on. The velocity of the last ball is