Block A weighs `4 N` and block weigh `8 N` The coefficient of kinetic friction is `0.25` for all surface find the force `F` to slide `B` at a constant speed when (a)`A` rest on `B` and moves with it (b) `A` is held at rest and (c )`A and B` are connected by a light cord passing over a smooth putting as shown in fig 7.31 (a - c) restively.

Options

A. `2 N`
B. `3 N`
C. `4 N`
D. `5 N`

Answer

d

Explanation

`F = f_(l_1) + f_(l_2) + T, T = f_(l_1)`
`F = 2f_(l_1)+ f_(l_2) = 3 N`