Question

An air craft flight at an attitude of 320m it fire a rocket with the initial velocity of 300km/h how long does it take the rocket to reach the ground

Answer 1

$$L=v_0\sqrt{2H/g}\\ =(300\div3.6\rm\: m/s)\sqrt{2*320\:m/9.8\: m/s^2}=673\: m$$