Related Rates

[Shay10825]

Hi. I need some help.

A baseball diamond is a 90 foot square. A player approaches 3rd base at a rate of 28 feet per second at the instant he is 30 feet from 3rd base. Find the rate of change of the player's distance from homeplate.

So df/dt= 28

But I don't know where to go from here.

[HallsofIvy]

First draw a picture!

Draw a square marking, in particular, homeplate, third base, and the position of the runner. Do you see a right triangle? Right down the Pythagorean triangle using variables for the distance from the runner to homeplate and distance of the runner from third base and 90 as the distance from third base to homeplate. Now differentiate with respect to time.