9709 P42 - Mar 2022 - Q7
3384
A bead, A, of mass 0.1 kg is threaded on a long straight rigid wire which is inclined at \(\sin^{-1}\left(\frac{7}{25}\right)\) to the horizontal. A is released from rest and moves down the wire. The coefficient of friction between A and the wire is \(\mu\). When A has travelled 0.45 m down the wire, its speed is 0.6 m s\(^{-1}\).
(a) Show that \(\mu = 0.25\).
Another bead, B, of mass 0.5 kg is also threaded on the wire. At the point where A has travelled 0.45 m down the wire, it hits B which is instantaneously at rest on the wire. A is brought to instantaneous rest in the collision. The coefficient of friction between B and the wire is 0.275.
(b) Find the time from when the collision occurs until A collides with B again.
