Question

A ball thrown directly from a roof 52m high reaches the ground.what is the initial velocity

Answer 1

The key to these type of questions is finding t first like this because it is the same for the vertical and horizontal components  you can use    

s=ut+1/2 at²        

 Since acceleration a is zero in the horizontal component this becomes    

s=ut

  We know s (given) and we know t (from part A) so you can go on and calculate u.  For the last part we are dealing with only the vertical components so we can use v²=u²+2as