00:01
In this question, i have a cylindrical tank that's standing upright with one circular base on the ground, and it has a radius of 20 centimeters.
00:14
I want to know how fast does the water level in the tank drop when the water is being drained at 25 cubic centimeters per second.
00:24
So i have a cylinder.
00:27
What do i know about its volume? the volume of a cylinder is pi r squared times the height.
00:36
Now, the radius in this case is 20, and the radius isn't changing.
00:42
So i can plug that in right away.
00:45
My volume is pi times 20 squared times the height, or equivalently, my volume is 400 pi times h.
00:59
They said that the water was being drained at 25 cubic centimeters per second.
01:06
That's the rate of change of the volume with respect to time.
01:11
My dv dt is negative 25.
01:17
Now, i want to know how fast does the water level in the tank drop.
01:22
So i want to know what's my dh dt...