Consider three blocks placed one over the other as shown in Fig. Let as now pull the blocks with the force of magnitudes `18 N, 100 N` and `15 N` Take `m_(1) = m_(2) = m_(3) = 10 kg` If the coefficient of static and kinetic friction between all contacting surface are `mu_(g) = 0.2` respectively find the

(a) Acceleration of the block s
(b) Friction at each surface

Answer

`A = (1)/(2)ms^(-2)`

Explanation

Let all the blocks move together with common acceleration toward right , then
`a = (100 -25)/(30) = 2ms^(-2)`
Friction between A and B
`f_(l_1) = 0.3 xx 10 g = 30 N`
`f_(k_1) = 0.2 xx 10 g = 20 N`
Between B and C
`f_(l_2) = 0.3 xx 20 g = .60 N`
`f_(k_2) = 0.2 xx 20 g = 40 N`
Let us find friction between A and B

`a = (25-20)/(10) = (1)/(2)ms^(-2)`
For this let as friction between B and C

`f_(2) - 15 = 10a_(2)`
`f_(2) = 47.5 N`(possible)
so fimally acceleration of `A = (1)/(2)ms^(-2)`
acceleration of B and C `= 3.25ms^(-2)`