A ball of 0.1 makes an elastic collision with a ball of unknown mass that is initially at rest. If the 0.1 kg ball rebounds at one third of its original speed, what is the mas of the other ball ?

Explanation

For elastic collision,
`v_1=((m_1-m_2)u_1+2m_1u_2)/(m_1+m_2)`
[ `m_2`= mass of the other ball `v_1`=final velocity of the ball of mass 0.1 kg]
Now, `m_1=0.1 kg, u_1=v,u_2=0,v_1=-v/3`
`therefore -v/3=((0.1-m_2)v+0)/(0.1+m_2)`
`or, -vxx0.1-vm_2=0.3xxv-3vm_2`
`or, m_2=0.2kg`