Problems

A wedge of mass \(km\) has the shape (in cross-section) of a right-angled triangle. It stands on a smooth horizontal surface with one face vertical. The inclined face makes an angle \(\theta\) with the horizontal surface. A particle \(P\), of mass \(m\), is placed on the inclined face and released from rest. The horizontal face of the wedge is smooth, but the inclined face is rough and the coefficient of friction between \(P\) and this face is \(\mu\).

1. When \(P\) is released, it slides down the inclined plane at an acceleration \(a\) relative to the wedge. Show that the acceleration of the wedge is \[ \frac {a \cos\theta}{k+1}\,. \] To a stationary observer, \(P\) appears to descend along a straight line inclined at an angle~\(45^\circ\) to the horizontal. Show that \[ \tan\theta = \frac k {k+1}\,. \] In the case \(k=3\), find an expression for \(a\) in terms of \(g\) and \(\mu\).
2. What happens when \(P\) is released if \(\tan\theta \le \mu\)?

\(\,\)

A smooth hemispherical bowl of mass \(2m\) is rigidly mounted on a light carriage which slides freely on a horizontal table as shown in the diagram. The rim of the bowl is horizontal and has centre \(O\). A particle \(P\) of mass \(m\) is free to slide on the inner surface of the bowl. Initially, \(P\) is in contact with the rim of the bowl and the system is at rest. The system is released and when \(OP\) makes an angle \(\theta\) with the horizontal the velocity of the bowl is \(v\)? Show that \[3v=a\dot{\theta}\sin\theta \] and that \[ v^{2}=\frac{2ga\sin^{3}\theta}{3(3-\sin^{2}\theta)}, \] where \(a\) is the interior radius of the bowl. Find, in terms of \(m,g\) and \(\theta,\) the reaction between the bowl and the particle.