Hello OijlYou don't give us enough detail for me to give you a specific answer, but these are the principles you should use:

1. If you know that a body starts with velocity , and it travels a distance , in time , with an acceleration , then

Obviously, if your weights start from rest, then , and the equation is simply

2. If the tension in the string is (upwards) and there is a weight force downwards, and the acceleration is (downwards) then

Resolve downwards:

If you know and , this will give you the tension, .

Grandad