Two particles, \(P\) and \(Q\), with masses \(m\) and \(2 m\) respectively, are moving in the same direction along the same straight line when they collide directly. Immediately before they collide, \(P\) is moving with speed \(4 u\) and \(Q\) is moving with speed \(u\). Immediately after they collide, both particles are moving in the same direction and the speed of \(Q\) is four times the speed of \(P\).
Find the speed of \(Q\) immediately after the collision.
Find the magnitude of the impulse exerted by \(Q\) on \(P\) in the collision.