Question

a conical vessel of semi-vertical angle of 30degrees is held with vertex downwards and its axis vertical.water enters at the rate of 2cm^2 per minute .find the rate at which the water level is rising when the depth of the water is 4cm and the rate at which the plane surface area is increasing at this instant

Answer 1

At first glance I felt its easy. But later I found the difficult part of it. I can give you the link where you can find some clue. If you still not able to solve, I will be helping.

http://mathafou.free.fr/pbm_en/sol227.html

in this, look at the part "A frustum" (in detail)