Q. A $20\ kg$ block is initially at rest on a rough horizontal surface. A horizontal force of $75\ N$ is required set the block in motion. After it is in motion, a horizontal force of $60\ N$ is required to keep the block moving with constant speed. The coefficient of static friction is
A) $0.38$
B) 0.44
C) 0.52
D) 0.60
Explanation
(a) Coefficient of friction $\mu_{s} = \frac{F_{1}}{R} = \frac{75}{mg} = \frac{75}{20 \times 9.8} = 0.38$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.