Block B rests on a smooth surface .The coefficient of static friction between A and B is `mu = 0.4` where `F = 30 N` then

Acceleration of upper block is

Options

A. `3//2 ms^(-2)`
B. `6//7 ms^(-2)`
C. `4//3 ms^(-2)`
D. `3//7 ms^(-2)`

Answer

B

Explanation

For upper block
`a_(max)= mg = 4ms^(-2)` and `f_(max) = 40 N`
a. when `F = 30N`,as `F ltf_(max)`
so both blocks will move togather
`:. A = (F)/(M +m) = (30)/(15)= (6)/(7)ms^(-2)`
b. when `F = 250 N`
For upper block: `250 - 40 = 10a_(1)`
`210 = 10a_(1) rArr a_(1) = 21ms^(-2)`
For block
`a_(2) = (40)/(25)= (8)/(5)ms^(-2)`