Figure shows a system of four pulleys with two masses `m_(A) =3kg` and `m_(B)=4 kg`. At an instant force acting on block A if block `B` is going up at an acceleration of `3 m//s^(2)` and pulley `Q` is going down at an acceleration of `1 m//s^(2)` is
.

Options

A. (a)7 N acting upward
B. (b)7 N acting downward
C. (c)10 N acting upward
D. (d)10 N acting downward

Answer

B

Explanation

`implies 3 = (a_(1) + 0)/(2) implies a_(1)` = (acc of string between p `a_(1) = 6`
`implies 1 = (a_(2) - 6)/(2) implies a_(2)` = (acc of string between Q)
= `8 m//s^(2)`
`implies a = (8 - 1)/(2) = 3.5 m//s^(2)` i.e., acc of A.
`implies` Net force on `A = 3.5 xx 2 - 7N` downwards