Question

Radar tracking station O is 40 km away from a ship at Point A. The ship travels east 45 km to point C at 30 km/h. How long will the ship be on the radar with a 20 km radius?

Answer 1

first, let's find the time where the ship arrives to point C
t=d/V, t= 45/30=1.5h
if the ship's departure time is at 1.5h, on the point C, let 's find its arrival to the point O, V=D/Dt, Dt=tfinal-tinitial
Dt=D/V= 20/30=0.6h=t final -t initial, implies t final=0.6+t initial=0.6+1.5=2.1h

so the ship will be on the radar at 2.1h,