A small ball is projected with speed 15 m/s at an angle of 60 degrees above the horizontal. Find the distance from the point of projection of the ball at the instant when it is travelling horizontally.

If we break down the velocity vector into its x and y components, then the point at which the ball would be moving horizontally is the point where the y velocity is zero. The y velocity decreases initially due to gravity. V_y = 15m/s * sin(60deg) = 13 (approx). Therefore, the time when the ball would move horizontally is => t_h = V_y/g = 1.3 s(approx). V_x = 15m/s * sin(30) = 7.5 m/s . So the distance it would travel until it is horizontal is : d = V_x*t = 9.75m(approx)