The jet plane is flying at a speed 1000 km/h and the tank is moving at 40 km/h in the same direction. The relative horizontal speed of the two is 960 km/h.
The height of the jet when the bomb is dropped is 1200 m or 1.2 km. The time (t) taken by the bomb to reach the ground is given by `s = u*t + (1/2)*g*t^2` where u = 0 and s = 1200
`1200 = (1/2)*9.8*t^2`
`=> t = sqrt(12000/49) = (20*sqrt 30)/7` seconds
As the bomb falls down, for it to hit the tank, it should be dropped a horizontal distance D away from the tank where `D = 960*((20*sqrt 30)/7)/3600 = 4.17`
The bomb should be dropped 4.17 km away from the tank if it has to land on the tank.