Volume of a Spherical Raindrop: Differential Equation Solution

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SUMMARY

The discussion focuses on deriving a differential equation for the volume of a spherical raindrop as it evaporates over time. The volume is represented by the equation V = (4/3)πr³, while the surface area is S = 4πr². The initial attempt at a solution leads to the equation dV/dt = -k(4πr²), which simplifies to dV/dt = -k(3/r)V. The correct answer, however, is presented as -kV^(2/3), indicating a need to express the radius in terms of volume and adjust the constant k accordingly.

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Homework Statement



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.

Homework Equations



V = (4/3)πr3
S=4πr2

The Attempt at a Solution



dV/dt = -k(4πr2), k>0

Therefore dV/dt = -k(3/r)V

But the answer in the back of the book is

-kV2/3

How did they get that?
 
Physics news on Phys.org
in your solution, write r in terms of V and then absorb other constants in k.
 

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