Question

A military aircraft flying at an altitude of 1,000 m has launched a glide missile. If the missile landed 100m from the launch point, how fast was the aircraft flying?

Answer 1

The horizontal range

$$R=v_0\sqrt{2H/g}$$

Hence, the speed of the aircraft

$$v_0=R/\sqrt{2H/g}\\ =100/\sqrt{2*1000/9.8}=7\:\rm m/s$$