Three large sides blocks are kept stationary over one another as shown in the figure. A horizontal force of 20N is acting on the middle block as shown in the figure. Choose the correct statement.

Options

A. The acceleration of lowest block will be `4.5m//s^(2)`
B. The accleration of uppermost block will be `2m//s^(2)`
C. The frictional force between middle and lower block will be 12N
D. The frictional force between middle and upper block will be 2N.

Explanation

The situation is as shown in the figure. Drawing the free body diagram of each block `(f_(1))_("max")=mu_(1)N_(1)=(0.2)(1xx10)=2N`

`(f_(2))_("max")9=mu_(2)N_(2)=(0.8)(2xx10)=16N`
`(f_(3))_("max")=mu_(3)N_(3)=(0.3)(3xx10)=9N`
`f_(1)& f_(3)` will be kinetic and `f_(2)` will be static
Lower two blocks will move together wits `3m//s^(2)` while upper block will move with different acceleration `2m/ss^(2)`. Hence `f_(2)=15N`.