# Math Help - Need help with related rates

1. ## Need help with related rates

A water tank has the shape of an inverted cone with top radius 4 m and depth 10m. Waer is pored in to the tank at the rate of 5 m^3min^-1. How fast is the water rising when the depth of the water is 5 m?
i am not sure how to start

2. Originally Posted by supersaiyan
A water tank has the shape of an inverted cone with top radius 4 m and depth 10m. Waer is pored in to the tank at the rate of 5 m^3min^-1. How fast is the water rising when the depth of the water is 5 m?
i am not sure how to start
$V = \frac{\pi}{3} r^2 h$

get the volume of water in the tank in terms of $h$ ...

note that $\frac{r}{h} = \frac{4}{10}$

once you do that, take the derivative w/r to time and calculate $\frac{dh}{dt}$