In a figure shown mass of `A` and `B` is equal to `M` each. Friction between `B` and lowermost surface is negligible. Initially both the blocks are at rest. The dimensions of the block `A` are very small. A constant horizontal force `F` is applied on the blocks `B` and both the blocks start moving together without any relative motion. Suddenly, the block `B` encounters a fixed obstacle and comes to rest. The block `A` continues to slide on the block `B`. The block `A` just manages to reach the opposite end of the bolck `B`. What is the coefficient of friction between the two blocks? (Required length are shown in figure)

Options

A. `F//Mg`
B. `2F//Mg`
C. `F//2Mg`
D. none

Answer

A

Explanation

Velocity of upper block when lower bolck hits a obstacle,
`v=sqrt(2a)=sqrt(2.(F)/(2M))1=sqrt(F_(1)/(M))`
now after collision retardation of upper block w.r.t earth, `a=(muMg)/(M)=mug therefore v^(2)=u^(2)+2as`
`O=(Fl)/(M)-2mug"(1)/(2), rArrmu=(F)/(Mg)`