- #1

erik05

- 50

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Two people start from the same point. One walks east at 3 km/h and the other walks northeast at 2 km/h. How fast is the distance between them changing after 15 min? Ans: 2.125 km/h

Here's what I did:

dz/dt= 3 km/h

dx/dt= 2 km/h

dy/dt= ?

2 km/h * 0.25h= 0.5 km = x

3 km/h * 0.25h= 0.75 km= z

y= 0.5590

x^2 + y^2 = z^2

2x (dx/dt) + 2y (dy/dt)= 2z (dz/dt)

dy/dt= (z (dz/dt) - x (dx/dt))/ y

So I put all the numbers in and I get 2.236. ...and that's kind of close to the answer. Anyways, if anyone could point out what I'm doing wrong, it would be much appreciated. Thanks.