A bedroom bureau with a mass of 38 kg, including drawers and clothing, rests on

Question

A bedroom bureau with a mass of 38 kg, including drawers and clothing, rests on the horizontal floor. The coefficients of friction between the bureau and the floor are 0.45for static and 0.35 for kinetic. You pull on the bureau with a force 447 N at 20° above the horizontal. The bureau initially moves along the floor in the same general direction as you pull. (a) What is the maximum static friction force on the bureau (before it begins to move)?

(b) What is the acceleration of the bureau once it is in motion?

Explanation / Answer

mass m = 38 kg The coefficients of static friction between the bureau and the floor u = 0.45 The coefficients of kinetic friction between the bureau and the floor u ' =0.35 applied force F = 447 N angle ,theta = 20° (a) the maximum static friction force on the bureau f = u [ mg + F sin 20 ] f = 0.45 [ 372.4 +152.88 ] = 236.37 N (b) kinetic fricition force f ' = u ' [ mg + F sin 20 ] = 183.84 N Applied force along horizontal direction = F cos 20 = 420 N the acceleration of the bureau once it is in motion a = net force / mass a = ( 420 - 183.84 ) / 38 = 6.215 m / s^ 2

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