A motor is fixed inside a box which is moving upwards with velocity `5 m//s`. String is winding at the rate `3 m//s` Then the velocity of block A will be.

Options

A. 2.5 m/s downwards
B. 5 m/s downwards
C. 1 m/s downwards
D. 2 m/s downwards

Answer

C

Explanation

Velocity of a point on spring near motor
`V_(M) = 5m//s` upwards `- 3m//s` downwards
`= 2m//s` upwards
From constrant relation
`(V_(A))/(V_(M))=(T_(M))/(T_(A))=(T)/(2T)`
`rArr V_(A) = (V_(M))/(2) = (2)/(2) = 1m//s` downwards.