11. A golfer on a level fairway hits a ball at an angle of 21? To the horizontal and it travels 102 yd before striking the ground. He then hits another ball from the same spot with the same speed but at a different angle. This ball also travels 102 yd. At what angle was the second ball hit?

Use s = ut+\frac12 at^2 to find the time of flight in the first case, using the vertical component in terms of v (the velocity with which the golf ball left the tee). Then, use s= ut in terms of the horizontal component and use the time you got initially to get an equation in v only.

Once you get v, take s = ut+\frac12 at^2 and s = ut again but with angle theta and a new t. With those two equations and two unknowns (t and theta), find theta, the angle with which the second golf ball was projected.