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Physics · LAWS OF MOTION
हिन्दीA block of mass \( 5\text{ kg} \) rests on a rough horizontal surface with coefficients of static friction \( \mu_s = 0.4 \) and kinetic friction \( \mu_k = 0.3 \). A horizontal pulling force of \( 15\text{ N} \) is applied to the block. Taking \( g = 10\text{ m/s}^2 \), the magnitude of the frictional force exerted by the surface on the block is:
Correct answer · Option 4
\( 15\text{ N} \)
Explanation
Maximum static friction available: \( f_{s,\text{max}} = \mu_s m g = 0.4 \times 5 \times 10 = 20\text{ N} \). Since applied force \( F = 15\text{ N} < 20\text{ N} \), the block remains at rest and static friction adjusts to equal the applied force, i.e., \( f_s = 15\text{ N} \).
