A is a fixed point at a height H above a perfectly inelastic smooth horizontal plane. A light inextensible string of length L (>H) has one end attached to A and other end to a heavy particle. The particle is held at the level of A with string just taut and released from rest. Find the height of the particle above the plane when it is next instantaneously at rest.

http://lh4.google.com/rahul92781/R8FZ3dD9JhI/AAAAAAAAAD4/Uzhld1qvycs/collision.JPG

I don't quite understand the question, could you illustrate it?

If L>H, the particle will be at rest on the plane.

If L>H, the particle will be as rest on the plane.
This was the problem I was having too.