Question

Given in the figure are two blocks A and B of weight 20 N and 100 N, respectively. These are being pressed against a wall by a force F as shown. If the coefficient of friction between the blocks is 0.1 and between block B and the wall is 0.15, the frictional force applied by the wall on block B is: [JEE MAIN 2015] 2 ODN A B 2011

JEE/Engineering Exams

Physics

Solution

240

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In vertical direction, weights are balanced by frictional forces. Consider ( mathrm{FBD} ) of block ( mathrm{A} ) and ( mathrm{B} ) as shown in diagram below. As the blocks are in equilibrium, balance forces are in horizontal and vertical direction. For the system of blocks ( (mathrm{A}+ ) B). ( F=N ) For block ( A, F_{A}=20 mathrm{N} ) and for block ( B ) [ F_{B}=F_{A}+100=120 N ]