A small coin of mass 40 g is placed on the horizontal surface of a rotating disc. The disc starts from rest and is given a constant angular acceleration α = 2 rad s - 2 . The coefficient of static friction between the coin and the disc is μ s = 3 / 4 and the coefficient of kinetic friction is μ k = 0.5 . The coin is placed at a distance r = 1 m from the centre of the disc. The magnitude of the resultant force on the coin exerted by the disc just before it starts slipping on the disc is :

Question

A small coin of mass 40 g is placed on the horizontal surface of a rotating disc. The disc starts from rest and is given a constant angular acceleration α = 2 rad s - 2 . The coefficient of static friction between the coin and the disc is μ s = 3 / 4 and the coefficient of kinetic friction is μ k = 0.5 . The coin is placed at a distance r = 1 m from the centre of the disc. The magnitude of the resultant force on the coin exerted by the disc just before it starts slipping on the disc is :, 0 . 2 N, 0 . 3 N, 0 . 4 N, 0 . 5 N

MARKS App · Accepted Answer

The friction force on coin just before coin is to slip will be : f = μ s mg Normal reaction on the coin ; N = mg The resultant reaction by disk to the coin is = N 2 + f 2 = mg 2 + μ s mg 2 = mg 1 + μ s 2 = 4 0 × 1 0 - 3 × 1 0 × 1 + 9 1 6 = 0.5 N

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