Question

A projectile is fixed at an angle of 15º to the horizontal with the speed v. If another projectile is projected with the same speed, then at what angle with the horizontal it must be projected so as to have the same range?

Answer 1

For same R and v, the sum of the two angles of projection is 90º. As one angle is of 15º, other should be 90º – 15º = 75º.