Question

At noon, ship A is 45 miles due west of ship
B. Ship A is sailing south at 5 mph while ship
B is sailing north at 15 mph.
At what speed is the distance between the
ships changing at 3:00 pm?

Answer 1

distance = ((20t)^2 + 45^2)^0.5

d(distance)/dt =
0.5*800t*(400t^2 + 2025)^-0.5
400t / (400t^2 + 2025)^0.5

plug t =3

1200 / (3600 + 2025)^0.5 = 1200 / 75 = 16

Answer 2

similar triangles again