Mathematics 9709 · AS & A Level · Probability

Probability — practice question

A uniform solid hemisphere, with weight $60\text{ N}$ and radius $0.8\text{ m}$, is in limiting equilibrium on a rough horizontal plane with its curved face in contact with the plane. The hemisphere’s axis of symmetry makes an angle $\theta$ with the horizontal, where $\cos\theta = 0.28$. A horizontal force of magnitude $P\text{ N}$ is applied at the lowest point of the circular rim to keep the hemisphere in equilibrium (see diagram).
(i)[3]

Show, by calculation, that $P = 8.75$.

(ii)[2]

Find, from the information given, the coefficient of friction between the hemisphere and the plane.

Worked solution & mark scheme

This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: An attempt to use moments, e.g. $60(\tfrac13\times0.8)\times0.28 = P(0.8-0.8\times0.28)$

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