Two blocks: 3 kg ON TOP of 5 kg, μ between them = 0.5. The 5 kg block on smooth floor. Horizontal force F = 20 N applied to TOP 3 kg block. Do they move TOGETHER?
AYes — required friction (12.5 N) is below max (15 N)
BNo, top block slides
CBoth at rest
DCannot determine
Answer & Solution
Correct answer: A. Yes — required friction (12.5 N) is below max (15 N)
Combined acceleration if moving together: a = 20/(3+5) = 2.5 m/s². For bottom block to accelerate at 2.5 m/s², friction needed = 5 × 2.5 = 12.5 N. Max friction available = μ × m_top × g = 0.5 × 3 × 10 = 15 N. Since 12.5 N < 15 N max, friction is sufficient → they MOVE TOGETHER.
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