Two smooth uniform spheres \(A\) and \(B\), of equal radii, have masses \(m\) and \(5m\) respectively. Sphere \(A\) moves on a smooth horizontal surface with speed \(u\) and collides with sphere \(B\), which is initially at rest.

Immediately before impact, the direction of motion of \(A\) makes an angle \(\theta\) with the line of centres. After the collision, the kinetic energies of \(A\) and \(B\) are equal. The coefficient of restitution between the spheres is \(\dfrac12\).

Find \(\tan\theta\).