Scooterist A starts from the origin O(0,0) at t=0 and rides with a constant velocity 20m s−1 due east. At the same instant scooterist B is at the point Q(100m,60m) and moves with a constant velocity 15m s−1 due south.
(i) Determine the velocity of A as observed from B, giving its magnitude and direction with respect to the east.
(ii) After how much time will the two scooterists have the same y–coordinate? (Assume the velocities remain unchanged.)