Arbeid - enkelt spørsmål

[Guest]

Hei,

Jeg ser på en oppgave som lyder slik:
Water fills a tank in the shape of a right-circular cone With top radius 3 m and depth 4 m. How much work must be done (against gravity) to pump all the water out of the tank over the top edge of the tank?

Solution
A thin, disk-shaped Slice of water at height h above the vertex of the tank has radius r, where radius r= 3/4 h by similar triangles. The volume is
dV= pi r^2dh= 9/16 pi h^2 dh

osv osv

Det jeg lurer på er hvordan kan radiusen være r=3/4h???

Takk

[Janhaa]

formlike trekanter;

[tex]r/3 = h/4[/tex]