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20. A disc revolves in a horizontal plane with a steady speed of 3r.p.s. A coin just keeps on rotating with the disc when placed 2 cm from the axis of rotation The coefficient of friction between the coin and disc is : (A) 0.5 (C) 0.75 (B) 0.65 (D) 07.

Answer»

tion:from the given data CENTRIFUGAL force should be balanced by FRICTIONAL force =>μmg=mrw^2 here w = 3 × 2π = 6π , R = 2 cm thus μ= rw^2 /g = 2/100 × 36π^2 ÷10 = 0.702 NEARLY 0.7



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