Question

A ball with a mass of `5kg` moving at `2 m/s` hits a still ball with a mass of `9 kg`. If the first ball stops moving, how fast is the second ball moving?

Answer 1

`1.111 \ \text{m/s}`

Explanation:

One ball of mass `m_1=5`kg moving at `u_1=2\ m/s` hits another ball of mass `m_2=9` kg at rest `u_2=0`. After collision, the first ball stops i.e. `v_1=0` & second ball moves with a velocity of `v_2` in the initial direction of first ball then

By the conservation of momentum in moving direction of first ball

`\text{momentum before collision}=\text{momentum after collision}`

`m_1u_1+m_2u_2=m_1v_1+m_2v_2`

`5(2)+9(0)=5(0)+9v_2`

`9v_2=10`

`v_2=10/9`

`v_2=1.111 \ \text{m/s}`