Related rates of change are killing me!


by KingNothing
Tags: killing, rates
KingNothing
KingNothing is offline
#1
Mar16-06, 03:25 PM
P: 949
Hi. I am getting absolutely embarassed by these related rates problems. Here is one that I simply keep getting wrong:

The volume of an expanding sphere is increasing at a rate of 12 cubed cm per second. When the volume is [tex]36\pi[/tex], how fast is the surface area increasing?

[tex]V=\frac {4*pi*r^3}{3}[/tex][tex]S=4*pi*r^2[/tex]
(how the heck do you use pi in latex? I know it's \pi, but that doesn't work right when Iput it in!)

[tex]\frac {dV}{dt}=4 \cdot \pi \cdot r^2 \cdot \frac {dr}{dt}[/tex]
Since volume is [tex]36 \cdot \pi[/tex], [tex]r=3[/tex]. Correct?
Phys.Org News Partner Science news on Phys.org
Simplicity is key to co-operative robots
Chemical vapor deposition used to grow atomic layer materials on top of each other
Earliest ancestor of land herbivores discovered
Doc Al
Doc Al is offline
#2
Mar16-06, 03:30 PM
Mentor
Doc Al's Avatar
P: 40,875
Start by finding [itex]dV/dt[/itex] and [itex]dS/dt[/itex] in terms of r and [itex]dr/dt[/itex]. (Hint: Chain rule)


Register to reply

Related Discussions
Related rates Engineering, Comp Sci, & Technology Homework 0
Related rates Calculus & Beyond Homework 2
Related rates Introductory Physics Homework 2
Related rates of change! (2 problems) Introductory Physics Homework 8
related rates of change Introductory Physics Homework 4