Two block A and B of masses `6 kg` and `3 kg ` rest on a smooth horizontal surface as shown in figure If coefficient of friction between A and Bb is `0.4` the maximum horizontal force which can make them move without separation is

Options

A. `72 N`
B. `40 N`
C. `36 N`
D. `20 N`

Answer

c

Explanation

Maximum friction force on block B is
`mu m_(B)g = 0.4 xx 3 xx 10 = 12N`
Hence, maximum acceleration `= (12)/(3) = 4ms^(-1)`
Hence , maximum force
`F = (m_(A) + m_(B)) a = (6 + 3) xx 4 = 36 N`
Afiber We can also apply the formula discussed in pervious problem by putting `mu_(2)= 0and mu_(1) = 0.4`