Calculating Projectile Motion and Speed: Vertical and Horizontal Components

[texmex]

A projectile is to be fired so that it just clears an obstacle 80m high at its maximum height.
http://img167.imageshack.us/img167/5729/physicszh7.jpg
a) by considering the vertical motion only, calculate the vertical speedand the time taken to reach its maximum height
b) if the distance between A to B is 100m, calculate the horizontal speed with which the ball was thrown.
c) Hence find v and Θ.


totally stuck at this, any help much appricated.

 

[hage567]

Have you tried anything? What equations might be used? What can you say about the vertical component of the velocity at maximum height?

 

[texmex]

the farthest i got, was putting in the right angle, and as for equations that could be used, i think it may have something to do with - Vvertical= vsinΘ. not entirely sure though.

 

[hage567]

That would be the initial vertical velocity (is that a negative sign?). What is the vertical velocity at the instant of maximum height?