A fighter plane flying horizontally at an altitude of 1.5 km with speed 720 km h-l passes directly overhead an anti-aircraft gun. At what angle from the vertical should the gun be fired for the shell with muzzle speed 600 m s-l to hit the plane. (Take g: l0 m s-2)

Here,Speed of the plane, v = 720 km h-1    = 720 × 518 ms-1 = 200 ms-1Speed of the shell, u = 600 ms-1Let the shell will hit the plane at L after time t if fired at an angle θ with the vertical from O.For hitting, horizontal distance travelled by the plane = horizontal distance travelled by the shell.i.e., v ×t = u sin θ ×t    sin θ = vu= 200 ms-1600 ms-1 = 13     θ = sin-1(13)