A light ball $B$ with mass $0.2\text{ kg}$ is fastened to fixed points $P$ and $Q$ by two light inextensible strings of the same length. $P$ lies directly above $Q$, the strings are taut, and each one makes an angle of $60^\circ$ with the vertical. $B$ travels at constant speed in a horizontal circle of radius $0.6\text{ m}$.
(i(a))[2]
If the tension in string $PB$ is $7\text{ N}$, calculate the tension in string $QB$.
(i(b))[3]
Calculate the speed of $B$.
(ii)[4]
If instead $B$ is travelling with angular speed $7\text{ rad s}^{-1}$, calculate the tension in the string $QB$.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Resolves vertically, e.g. $T\cos60=7\cos60-0.2g$” …