A bullet of mass `10 kg` moving horizontally at a speed `140 m//s` strikes a block of mass `100 g` attached to a string like a simple pendulum. The bullet penetrates the block and emerges on the other side. If the block rises by `80 cm` , find final velocity of bullet.

Explanation

By the momentum conservation
`(10)/(1000) xx 140 + (100)/(1000) xx 0 = (100)/(1000) v_(1) + (10)/(1000) v_(2)`
`140 = 10 v_(1) + v_(2)` (i)
For the block : `0 = v_(1)^(2) - 2g((80)/(100)) rArr v_(1) = 4 m//s` in (i)
`140 = 10 xx 4 + v_(2)`
`v_(2) = 100 m//s`
Final velocity of bullet` = 100 m//s`