Airplanes A and B are flying with constant velocity in the same vertical plane at angles 30∘ and 60∘ with respect to the horizontal respectively as shown in figure. The speed of A is 1003ms−1. At time t=0s, an observer in A finds B at a distance of 500m. This observer sees B moving with a constant velocity perpendicular to the line of motion of A. If at t=t0, A just escapes being hit by B, t0 in seconds is