(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!

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Simple differential eqn's question

**Physics Forums | Science Articles, Homework Help, Discussion**