(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Water is flowing from a major broken water main at the intersection of two streets. The resulting puddle of water is circular and the radius r of the puddle is given by the equation r = 5t feet, where t represents time in seconds elapsed since the main broke.

When the main broke, A runner was 6 miles east and 5000 feet north of the intersection. The runner is due west at 17 feet per second. When will the runner's feet get wet?

3. The attempt at a solution

Not exactly sure how to solve this problem but here's all I got:

- Triangle, on the x-axis labelled it 31, 680 ft, on the y-axis labelled it 5,000 ft. The hypotenuse is then 32, 072.1437 ft.

- Diffierientiated x^2 + y^2 = r^2 and got 2x dx/dt + 2y dy/dt = 2 r dr/dt

- Looked back at the equation r = 5t, found r' to be 5, so dr/dt =5

- Just pluged the 5 back in like any algebra problem and got

5,000dx/dt + 31,680(-17) = 5(32072.1437)

dx/dt = 139. 784144

Not sure where I went wrong, I plugged the equation back into r = 5t and got 27.95 -- the book says 25.4154041 minutes so there's something wrong here

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# Homework Help: (Easy) Calculus problem dealing with a runner

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