Question

8(d). A crate of drinks of mass 20 kg is placed on a plane inclined at 30° to the horizontal. If the crate slides down with a constant speed, calculate: (i) the coefficient of kinetic friction; (ii) the magnitude of the frictional force acting on the crate. [g = 10 ms⁻²]

Accepted Answer

Since the crate slides at constant speed, the frictional force balances the component of gravity along the incline: mg sinθ = F_r = μR, where R = mg cosθ.
(i) For constant-speed sliding down a rough incline, μ = tanθ = tan30° = 0.58.
(ii) F_r = μR = μ(mg cosθ) = 0.58 × 20 × 10 × cos30° ≈ 100.5 N.

WAEC Physics 2015 Theory — Question 11

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