A 4.0-kg block starts from rest and slides 5.0 m down a plane inclined at 60^o to the horizontal. The coefficient of kinetic friction between the surface and the block is 0.20. The work done by friction on the block is A) 98.0 J B) 19.6 J C) 3.92 J D) 3.40 J E) 64.0 J

Question

Quizplus · Accepted Answer

To find the work done by friction, we need to find the force of friction and the distance it acts over. The force of friction is given by the coefficient of kinetic friction (0.20) multiplied by the normal force, which is equal to the weight of the block perpendicular to the plane. This weight is mg*cos(60°) = 4.0 kg * 9.81 m/s^2 * 0.5 = 19.62 N. So the force of friction is 0.20 * 19.62 N = 3.92 N. The distance over which this force acts is the distance the block travels down the plane, which is 5.0 m. So the work done by friction is the force of friction multiplied by the distance it acts over, which is 3.92 N * 5.0 m = 19.6 J. Therefore, the answer is B.

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