A ball of mass m makes a head-on elastic collision with a second ball (at rest) and rebounds with a speed equal to 0.370 its original speed. What is the mass of the second ball?

The mass of the second ball is

Explanation:

From the question we are told that  

     The mass of the first  ball is  m

Let assume

    The original speed of the first ball is  

     The rebound speed is  

According to the law of momentum conservation

The  second ball is at rest so  

And the negative sign shows that it is a rebound velocity

=>  

Now  we are told that the collision is  elastic, this means that the velocity of approach will be equal to the velocity of separation

  So  

=>      

=>      

substituting this into equation above

=>    

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