Airplane A and B are flying with constant velocities I the same vertical plane at angles 30° and 60° with respect to the horizontal . The speed of A is 100√3 m/s. At time t=0 , an observer in A finds B at a distance if 500m. This observer sees B moving with a constant velocity perpendicular to the line of motion of plane A. If at t=t•, A just escapes being hit by B, t• in seconds is


