# Related rate problem

• Nov 24th 2009, 02:44 PM
Related rate problem
Since this forum was so helpful on my last question I have another one I'm struggling with.....

Phoebe is going east on Alamo street at 40 ft./second, meanwhile Calvin is going south on heights street at 30 ft./second. We need to determine the straight line distance between them. Then, when Phoebe is 200 feet from the intersection, Calvin is 600 ft. from the intersection. At this time is the straight-line distance between them increasing or decreasing? At what rate?

Thanks!
• Nov 24th 2009, 03:25 PM
Scott H
The question appears to be ambiguous. How do we know whether Calvin and Phoebe are approaching or leaving the intersection?

At any rate, if $\displaystyle s_C$ represents Calvin's distance from the intersection and $\displaystyle s_P$ represents Phoebe's distance, we are given that

\displaystyle \begin{aligned} \frac{ds_C}{dt}&=\pm 30\\ \frac{ds_P}{dt}&=\pm 40. \end{aligned}
• Nov 24th 2009, 04:29 PM
aidan
Quote: