Hi I have two questions that I'm stuck on. I don't want solutions but any hints/pointers would be much appreciated.

1) An object is projected vertically upwards with a velocity ofum/s, and afterts another object is projected upwards from the same point with the same velocity. Find, in terms ofu, t and gthe time which elapses between the second object's projection and the collision between the objects.

At first I tried finding the times when the displacements of equal, using (T+t) and t for A and B respectively. Then got nowhere...

2) A light string of lengthais attached to two points A and B on the same level and a distancebapart, whereb<a. A smooth ring of weight W is threaded on the string and is pulled by a horizontal force, P, so that it rests in equilibrium vertically below B. Show that the tension in the string is

[W(a^2 + b^2)]/(2a^2)

No idea on this one...any hints?