Two blocks $P$ of mass 4 kg and $Q$ of mass 6 kg are connected by a light inextensible string. The string passes over a smooth pulley fixed at the top of a rough inclined plane. The plane is inclined at an angle of $25^{\circ }$ to the horizontal. Block $P$ lies on the plane and $Q$ hangs freely from the pulley with the string taut. Block $P$ is released from rest and accelerates up the plane at 1.5 ms^-2.