# Defferentiation

• October 3rd 2011, 11:29 AM
leeubc22
Defferentiation
rocks are filling a cone at 72in^3 per min. during every interval of time the cone has a height, h, which is always 6 times the radius. what is the rate of change of the radius of the cone at the instant when the radius is 2in. the volume of the cone is
v=1/3 pie r^2 h.
• October 3rd 2011, 11:34 AM
skeeter
Re: Defferentiation
Quote:

Originally Posted by leeubc22
rocks are filling a cone at 72in^3 per min. during every interval of time the cone has a height, h, which is always 6 times the radius. what is the rate of change of the radius of the mound at the instant when the radius is 2in. the volume of the cone is
v=1/3 pie r^2 h.

$h = 6r$

$V = \frac{\pi}{3} r^2 \cdot (6r)$

simplify the volume equation, then take the derivative w/r to time. substitute in your given values and determine the value of $\frac{dr}{dt}$

btw, the greek letter $\pi$ is spelled pi ... "pie" is something you eat.
• October 3rd 2011, 11:36 AM
leeubc22
Re: Defferentiation
haha thanks. i was in a rush and wasn't paying attention