A body of mass 5 kg makes an elastic collision with another body at rest and continues to move in the original direction after collision with a velocity equal to 1/10th of its original velocity. Then the mass of the second body is

My answer is not matching , Can you tell me what mistake i am making ?

Question

A body of mass 5 kg makes an elastic collision with another body at rest and continues to move in the original direction after collision with a velocity equal to 1/10th of its original velocity. Then the mass of the second body is

My answer is not matching , Can you tell me what mistake i am making ?

anonymous · Answer

Conservation of linear momentum:
5(u)=5(u/10)+Mv

anonymous · Answer

Equation of coefficient of restitution :
e=1=$$(u/10-v)/u-0$$