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June 3rd, 2010, 09:11 AM  #1 
Member Joined: Feb 2008 Posts: 30 Thanks: 0  Related Rates Problem: Find rate that distance is changing.
A man walks north at 1.8m/s, a woman walks east at 2m/s. At what rate is the distance between them increasing after one minute if they leave from the same point at the same time. Attempt @ Work: dx/dt = 1.8m/s dy/dt = 2m/s Find dz/dt after 60 seconds. I made a triangle. 60 * 1.8 = 108m/s 60 * 2 = 120m/s Pythagorean Theorem 120^2 + 108^2 = z^2 z = ~161.44 x^2 + y^2 = z^2 Differentiate 2x * dx/dt + 2y * dy/dt = 2z * dz/dt Replace variables in [ 2(10(1.8 )+2(120)(2) ] / [2(161.44)] = 2.7 
June 3rd, 2010, 11:55 AM  #2 
Guest Joined: Posts: n/a Thanks:  Re: Related Rates Problem: Find rate that distance is changing.
Yep. That's what I get. Good show Unless we're both wrong, but I don't think so. 
June 5th, 2010, 04:34 AM  #3 
Senior Member Joined: Jan 2009 Posts: 344 Thanks: 3  Re: Related Rates Problem: Find rate that distance is changing.
Nice work It would be nice to visualize all this on an xy plane and it would be convenient to use dy/dt for the man moving north (along the y axis) and dx/dt for the woman moving east (along the xaxis) I'm just saying. 

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