Two blocks A and B of masses 6, kg and 3, kg rest on a smooth horizontal surface as shown in figure.

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4-2.Friction

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Two blocks $A$ and $B$ of masses $6\, kg$ and $3\, kg$ rest on a smooth horizontal surface as shown in the figure. If coefficient of friction between $A$ and $B$ is $0.4$, the maximum horizontal force which can make them without separation is ........ $N$

A

$72$

B

$40$

C

$36$

D

$20$

Solution

Frictional force on block $B$

$=\mu \mathrm{m}_{\mathrm{B}} \mathrm{g}=0.4 \times 3 \times 10=12 \mathrm{N}$

Hence, acceleration $=\frac{12}{3}=4 \mathrm{ms}^{-2}$

Hence, maximum force

$\mathrm{F}=\left(\mathrm{m}_{\mathrm{A}}+\mathrm{m}_{\mathrm{B}}\right) \mathrm{a}=(6+3) \times 4=36 \mathrm{N}$

Standard 11

Physics

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