So using the projectile equation I got ##a\sin (\alpha + \beta) = v\sin (\alpha + \beta)t + \frac{g\sin \beta t^2}{2}##
To find t we use the other projectile equation:
Since the horizontal velocity must be 0 for it to hit the ground perpendicularly we set the equation to be:
##0 = v\sin (\alpha...