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.
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Explanation:
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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