A 2 kg block A is placed on a 5 kg block B. Ground is smooth. A force 12 N acts towards right on A and a force 20 N acts towards right on B. Static friction is sufficient to prevent slipping. Friction on A is:
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Question

A 2 kg block A is placed on a 5 kg block B. Ground is smooth. A force 12 N acts towards right on A and a force 20 N acts towards right on B. Static friction is sufficient to prevent slipping. Friction on A is:

Options

G1 Physics · Accepted Answer

Common acceleration a = (12+20)/(2+5) = 32/7 m/s². For block A, 12 + f = 2(32/7). Thus f = 64/7 - 12 = -20/7 N. Hence friction on A is 20/7 ≈ 2.86 N towards left. The correct value is 2.86 N towards left.