A 2 kg block is placed on a 3 kg block. Ground is smooth and coefficient of static friction between them is 0.2. A horizontal force F is applied on the upper 2 kg block. Take g = 10 m/s². Maximum F for which both blocks move together is:
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Question

A 2 kg block is placed on a 3 kg block. Ground is smooth and coefficient of static friction between them is 0.2. A horizontal force F is applied on the upper 2 kg block. Take g = 10 m/s². Maximum F for which both blocks move together is:

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G1 Physics · Accepted Answer

If both move together, a = F/5. The lower 3 kg block is accelerated only by friction, so required f = 3F/5. Maximum friction between blocks is μₛm_top g = 0.2×2×10 = 4 N. Thus 3F/5 ≤ 4 ⇒ F ≤ 20/3 = 6.67 N.