Homework Help: calculus

Posted by rachel on Sunday, November 6, 2011 at 10:27pm.

water in a paper conical filter drips into a cup. let x denote the height of the water in the cup. if 10 in^3 of water are poured into the filter, find the relationship between dy/dt and dx/dt

so the paper filter is 4 inches tall
whith a radius of 2 inches. x is the height of the water in the cone.

the cup is 4 inches wide and y is the height of the water in the cup. please help! thanks(:

calculus - Steve, Monday, November 7, 2011 at 12:53pm
If the water in the filter is at depth x, with the surface of radius r,

x/r = 4/2 = 2
x = 2r
r = x/2

now, the volume of the water in the cup, plus that in the filter adds up to 10

cone: v = 1/3 pi r^2 x = pi/12 x^3
cup: v = pi r^2 y = 4pi y

pi/12 x^3 + 4pi y = 10

pi/4 x^2 dx/dt + 4pi dy/dt = 0

multiply by 4/pi to simplify a bit:

x^2 dx/dt + 16 dy/dt = 0

You can massage that into whatever form you need.

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