1. The problem statement, all variables and given/known data A projectile fired up into the air from the top of a 75m high cliff hits the ground 500m out from the base. Calculate the initial launch velocity (U), and launch angle (theta) of the projectile. 2. Relevant equations 1) v=u+at 2) v2=u2 +2as 3) s=ut+0.5at2 3. The attempt at a solution Consider up to be positive direction. Consider vertical component (y component) of motion for entire flight: a=-9.8 m/s2 s=-75m uy=Usin(theta) Sub into Eqn 3: -75=Usin(theta)t+0.5(-9.8)t2 #EQN A Consider horizontal component (x component) of motion for entire flight: a=0 s=500m ux=ucos(theta) Sub into Eqn 3: 500=ucos(theta)t #EQN B Now comes the problem... I have created 2 equations (A,B), but with 3 unknowns (u, theta,t). I think I need another equation ??? This is REALLY bugging me, please help. Thanks very much.