I'm stuck on this question:(adsbygoogle = window.adsbygoogle || []).push({});

"A man is sipping soda through a straw from a conical cup, 15 cm deep and 8 cm in diameter at the top. When the soda is 10 cm deep, he is drinking at the rate of 20 cm^3/s. How fast is the level of the soda dropping at that time?"

So you are given height = 15 cm, radius = 4 cm, and the derivative of the volume at height = 10 cm is 20 cm^3/s. It would appear that the question is asking for the derivative of height at 10 cm.

So volume of a cone is 1/3*pi*r^2*h, meaning, the derivative of that is:

dV/dt = (2*pi*r*dr/dt*h)/3 + (dh/dt*pi*r^2)/3

The only problem is that to find dh/dt, as the question is asking, we need to know dr/dt, and I can't think of anything I could do to find it. So perhaps I went about this question the wrong way or there is something I'm not seeing. Any help or guidance would be greatly appreciated, thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Related Rates Calculus Cone problem

**Physics Forums | Science Articles, Homework Help, Discussion**