A 10 kg object collides with a stationary 5 kg object and after collision, they stick together and move forward with velocity `4 ms^(-1)`. What is the velocity with which the 10 kg object hits the second one ? 

Options

A. `4 ms^(-1)`
B. `6 ms^(-1)`
C. `10 ms^(-1)`
D. `12ms^(-1)`

Answer

B

Explanation

Here `m_1 = 10 kg, m_2 = 5 kg, u_1 = ? , u_2 = 0, v = 4 m//s`
Applying the principle of conservation of linear momentum,
`m_1u_1 + m_2u_2 = (m_1 + m_2)v , 10 u_1 + 5 xx 0 = (10 + 5) 4`
`10 u_1 = 60 " or " u_1 = 60/10 = 6 ms^(-1)`.