A 15-g coin slides upward on a surface that is inclined at an angle of 15 degree

Question

A 15-g coin slides upward on a surface that is inclined at an angle of 15 degree above the horizontal The coefficient of kinetic friction between the coin and the surface is 0 28; the coefficient of static friction is 0.39. Find the magnitude of the force of friction when the coin is sliding. Express your answer using two significant figures. Find the magnitude of the force of friction after it comes to rest Express your answer using two significant figures. Find the direction of the force of friction after it comes to rest

Explanation / Answer

When moving, Magnitude of friction force = µk*N ; where N = normal rkn = m*g*cos 15 = 0.28 * 15*10^-3 * 9.8 * 0.966 = 0.04 N Since friction opposes motion. Hence direction of friction is down the incline. When it comes to rest, µs*N = 55 * 10^-3 N and mgsin15 = 38* 10^-3 So, mgsin15 < µs*N hence, friction force = m*g*sin15 = 0.038 N up the incline; ie, in direction opposite to mgsin15

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