A boy and a block, both of same mass, are suspended at the same horizontal level, from each end of a light string that moves over a frictionless pulley as shown. The boy start moving upward with an acceleration `2.5m//s^(2)` relative the rope. If the block is to travel a total distance 10m before reaching at the pulley, the time taken by the block in doing so is equal to:

Options

A. `sqrt(8(s`
B. `4s`
C. `(10)/(sqrt(2))s
D. `8s`

Answer

B

Explanation

Acceleration of boy and block will be same equal to `1.25m//s^(2) w.r.t.` ground. Hence
`10=(1)/(2)(1.25)t^(2)`
`rArr t=4sec.`