Astudent standing on a cliff that is a vertical height d = 8.0 m above the level ground throws a stone with velocity v0 = 21 m/s at an angle θ = 28 ° below horizontal. the stone moves without air resistance; use a cartesian coordinate system with the origin at the stone's initial position. (a) with what speed, vf in meters per second, does the stone strike the ground? (b) if the stone had been thrown from the clifftop with the same initial speed and the same angle, but above the horizontal would its impact velocity be different?