Students roll a snowball from a roof that makes an angle θ with respect to the horizontal. The snowball leaves the roof with speed V, at height H above the ground. A physics professor is standing a horizontal distance D away from the building; the professors head is a height h above the ground. Derive an expression for the initial speed V the snowball must have in order to hit the professors head. Then derive an expression for the speed with which the snowball actually hits the professor's head.