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
100√3 ms−1. At time
t=0 s, an observer in A finds B at a distance of 500 m. 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