# Derivations

• October 24th 2008, 01:51 PM
calculus shmalculus
Derivations
Air is being pumped into a spherical balloon so that its volume increases at a rate of 80cm^3/s . How fast is the surface area of the balloon increasing when its radius is 11cm ?

... i found the derivative of Surface Area to be 8*pi*r*(dv/dt)=(ds/dt)

i keep getting 7040*pi as my answer.. but its not correct.

• October 24th 2008, 01:55 PM
Jhevon
Quote:

Originally Posted by calculus shmalculus
Air is being pumped into a spherical balloon so that its volume increases at a rate of 80cm^3/s . How fast is the surface area of the balloon increasing when its radius is 11cm ?

... i found the derivative of Surface Area to be 8*pi*r*(dv/dt)=(ds/dt)

i keep getting 7040*pi as my answer.. but its not correct.

of course that's not correct, that's the wrong equation.

recall, the surface area is given by $A = 4 \pi r^2$ and the volume is given by $V = \frac 43 \pi r^3$
• October 24th 2008, 02:03 PM
calculus shmalculus
i know the equations for both..
what i am asking is if i need to derivate the surface area equation and if so ho would i go about doing that..
i have been attempting his problem for a while now..

ugh..
• October 24th 2008, 02:06 PM
Jhevon
Quote:

Originally Posted by calculus shmalculus
i know the equations for both..
what i am asking is if i need to derivate the surface area equation and if so ho would i go about doing that..
i have been attempting his problem for a while now..

ugh..