M4 June 2010 Q2

2. Two smooth uniform spheres \(S\) and \(T\) have equal radii. The mass of \(S\) is 0.3 kg and the mass of \(T\) is 0.6 kg. The spheres are moving on a smooth horizontal plane and collide obliquely. Immediately before the collision the velocity of \(S\) is \(\mathbf{u}_1\) m s\(^{-1}\) and the velocity of \(T\) is \(\mathbf{u}_2\) m s\(^{-1}\). The coefficient of restitution between the spheres is 0.5. Immediately after the collision the velocity of \(S\) is \((-\mathbf{i} + 2\mathbf{j})\) m s\(^{-1}\) and the velocity of \(T\) is \((\mathbf{i} + \mathbf{j})\) m s\(^{-1}\). Given that when the spheres collide the line joining their centres is parallel to \(\mathbf{i}\),

(a) find
(i) \(\mathbf{u}_1\),
(ii) \(\mathbf{u}_2\).
(6)

After the collision, \(T\) goes on to collide with a smooth vertical wall which is parallel to \(\mathbf{j}\). Given that the coefficient of restitution between \(T\) and the wall is also 0.5, find

(b) the angle through which the direction of motion of \(T\) is deflected as a result of the collision with the wall, (5)
(c) the loss in kinetic energy of \(T\) caused by the collision with the wall. (3)