Attempting a projectile motion question where initial and final speed is given but angle of elevation isn't. Need to find an equation for the vertical distance H travelled. I got the right answer using v^2 = u^2 + 2as substituting s=H and a=-9.8. However the mark scheme states that this SUVAT equation can't be used as this equation needs the vertical component of speed (as gravity only acts vertically) . The correct answer was to use conservation of energy principle ie initial KE = final KE + GPE. However if I use this energy equation I get the following: 1/2 mu^2 = 1/2 m v^2 - 2gH . Multiplying throughout by 2 and re-arranging this gives v^2 = u^2 + 2as !! In other words the conservation of energy equation gives me the SUVAT equation which I'm not supposed to use! Where is the mistake??