Two ships A and B are 10km apart on a line running south to north. Ship A farther north is streaming west at 20 km/h and ship B is streaming north at 20 km/h. Their distance of closest approach and how long do they take to reach it ?

When a ship A is observing relative to ship B , Velocity of ship b relative to Ship A = we can write From the velocity triangle ,In trianglex= shortest distance = Am=AB sin θ.: x = 10x sin 450 m = 5 √2 kmNow length BM = AB cosθ = 10 x  cos 450 m = 5√2 km