A bullet of mass `7g` is fired into block weighing `7kg`, which is free to move. Calculate initial velocity of bullet if the velocity of the block with the bullet inside is `0.7m//s`.

Explanation

Here, `m_(1)=7g=7xx10^(-3)kg`
`m_(2)=7kg, v_(1)=?, v_(2)=0`
`v=0.7m//s`
From `m_(1)v_(1)+m_(2)u_(2)=(m_(1)+m_(2))v`
`m_(1)v_(1)= (m_(1)+m_(2))v`
`v_(1)=((m_(1)+m_(2))v)/(m_(1))=((0.007+7)0.7)/(7xx10^(-3))=700.7m//s`