# B Finding Constant value K

1. Mar 16, 2017

Hi,
I'm working on a problem about a spherical balloon as its inflated slowly the radius of the balloon is in cm and the time is in seconds

dr/dt = k/r2

Now I know how to rearrange this equation using separable differentiation

r=3√3kt+c

However I would like to find the value of the constant K

For example the radius is 6cm and the radius is increasing at the rate of 5/36pi cm per second and I would like to rearrange the dr/dt=k/r2 to find the value of K

Any help would be appreciated

2. Mar 16, 2017

### phyzguy

You are given dr/dt (5/36pi cm per second) at a given r (6cm). Plug these into your first equation and solve for k.