A block of mass `m=2 kg` is placed on a plank of mass `M=10 kg` which is placed on a smooth horizontal plan The coefficient of friction between the block and the plank is `mu=1/3`. If a horizontal force f is applied an the plank, then find the maximum value of F for which the block and the plank move together. (Take `g=10m//s^2)`

Options

A. 30 N
B. 40 N
C. 120 N
D. none of the above

Answer

B

Explanation

`"Acceletration"" "a=F/(M+m)"--------"(1)`
`"To move together friction"=ma, mu mg= ma`
`1/3 xx 10=F/12, :. F=(12 xx 10)/3=40 N`