A bullet of mass m moving with a horizontal velocity u strikes a stationary wooden block of mass M suspended by a string of length L = 50 cm. The bullet emerges out of the block with speed `(u)/(4)`. If M = 6 m, minimum value of u so that the block can complete the vertical circle (take, g = 10 `ms^(-2)`)

Options

A. 10 `ms^(-1)`
B. 20 `ms^(-1)`
C. 30 `ms^(-1)`
D. 40 `ms^(-1)`

Answer

D

Explanation

From mometum conservaion,
`"mu"=m(u)/(4)+(6m)sqrt(5xx10xx0.5)`
Solving we get, u = 40 `ms^(-1)`