Physics

Problem

A block of weight

W

is pulled across a horizontal surface at constant speed by a force

F

applied by a rope that makes an angle

\theta

above the horizontal. The coefficient of kinetic friction between the block and the surface is

\mu_k

. Which expression gives the magnitude of the pulling force

F

? a)

F = \dfrac{\mu_k W}{\cos\theta - \mu_k\sin\theta}

F = \dfrac{\mu_k W}{\cos\theta}

F = \dfrac{\mu_k W}{\cos\theta + \mu_k\sin\theta}

F = \dfrac{\mu_k W}{\sin\theta + \mu_k\cos\theta}