Two pendulum bobs of mass m and 2m are attached to treads of length L suspended from a rigid support. Both the bobs are taken to a height H from the lowest point and then released so they collide elastically at the lowest point in their motion. Velocity of bob of mass m just after impact is $\frac{5}{3}\sqrt{\mathrm{ngH}}$ the value of $\mathrm{n}$ is ____ .