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

A spherical raindrop evaporates at a rate proportional to its surface area. Write a differential equation for the volume of the raindrop as a function of time.

2. Relevant equations

3. The attempt at a solution

The answer is dV/dt = -kV^(2/3), for some k > 0.

I don't really understand this answer. The question states the volume changes at a rate proportional to its surface area (A = 4*pi*r^2), but it seems from the answer it depends on volume V. Can someone help me understand how to get to this answer? And how do I know there is a constant k in there too? The problem never states it.. am I just supposed to know this somehow?

Thanks!

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# Homework Help: Simple differential eqn's question

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