Calculus: HELP PLEASE :)?

Question

At noon, ship A is 30 nautical miles due west of ship B. Ship A is sailing west at 23 knots and ship B is sailing north at 21 knots. How fast (in knots) is the distance between the ships changing at 4 PM? (Note: 1 knot is a speed of 1 nautical mile per hour.)

Answer 1

Let distance between the ships be y and time in hours after noon be x

y^2 = (30 + 23x)^2 + (21x)^2

y^2 = 970x^2 + 900

dy/dx = 970x(970x^2 + 900)^-0.5

when x = 4,

dy/dx = 30.27925247 knots

So the distance is changing at about 30 knots.

Answer 2

Unable to answer this question.  What direction is the tide and what is its speed?

A sailing ship needs wind - what direction is the wind and its speed.

If these ships were motor powered, then I could answer.

If both of these ships are sailing at "hull speed", then the ship going 21 knots is 246 feet long and the other one is 295 feet long.