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)` a) 4 N b) 8 N c) 12 N d) 10 N

Explanation

When t = 2 sec F = 4N
`f_(ms)=mu_(s)mg = 0.2xx4xx10=8N`
`therefore F lt f_(ms) therefore` friction = 4 N
When t = 5 sec F = 2 (5) = 10 N
`F gt f " " therefore` friction = 8 N.