A block of mass `4 kg` is placed on a rough horizontal force plane. A time dependent horizontal force `F = k t` acts on the block. Here `k = 2 Ns^(-1)`. The frictional force between the block and plane at time `t = 2 s` is `(mu = 0.2)`

Options

A. `4 N`
B. `8 N`
C. `12 N`
D. `10 N`

Answer

A

Explanation

`N = mg = 40N`
`muN = 0.2 xx 40 = 8 N`
`t = 2 s, F = 4 N`
`F lt mu N`
:. `f = F = 4 N`