At noon, ship A is 20 nautical miles...

Question

At noon, ship A is 20 nautical miles due west of ship B. Ship A is sailing west at 19 knots and ship B is sailing north at 18 knots. How fast is the distance between the ships changing at 4 PM? (Note: 1 knot is a speed of 1 nautical mile per hour.)

Answer 1

I drew-up the triangle. At 4hrs sipA went 76 knots. It started at 20 knots; so side "b"=96knots.

As for shipB at 4 hrs the distance is 72 knots; so that's side "a".

a^2+b^2=c^2.

5183+9216=14400^.5=120km

So at knots/hr the speed is 30.