Related rates porblem Please help.

Limits, differentiation, related rates, integration, trig integrals, etc.
Posts: 1
Joined: Sun Nov 11, 2012 5:20 pm

Related rates porblem Please help.

Postby dungas » Sun Nov 11, 2012 5:24 pm

I'm in grade 12 and this was given on a test and I had no clue how to solve it (it was a bonus question)

If two men are running away from each other at 45 degrees and man1 is running at 12 km/h and man2 is running at 10 km/h; How fast are they moving apart at 2.5 hours?

So I first made a drawing: Image
Is that correct?

I have no clue how to come up with an equation with respect to time.

Please help :confused:

Posts: 288
Joined: Sun Dec 14, 2008 11:07 pm

Re: Related rates porblem Please help.

Postby nona.m.nona » Sun Nov 11, 2012 6:33 pm

I would suggest labelling the two sides as "x" and "y", so their speeds are "dx/dt" and "dy/dt", respectively. The distance D is the vertical side's length. Then note that this is a right triangle, so x2 + D2 = y2 (assuming "y" is the hypotenuse). Differentiate, etc.

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