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Smazmbazm
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Homework Statement
Using line integrals, find the mass and the position of the center of mass of a thin wire in the shape of a half-circle [itex]x^{2} + y^{2} = r^{2}, x ≥ 0 [/itex] and [itex]-r ≤ y≤ r[/itex] if the linear density is [itex]ρ(x,y) = x^{2} + y^{2}[/itex]
The mass is given by the integral of the density along the curve while the center of mass is defined as
[itex]\frac{∫_{C} x ρ(x,y)ds}{∫_{C}ρ(x,y)ds}[/itex]
for the x co-ordinate and similarly for the y co-ordinate.
The Attempt at a Solution
My attempt was to substitute [itex]x^{2} = y^{2} - r^{2}[/itex] and [itex]y^{2} = x^{2} - r^{2}[/itex] into the density function to get [itex]ρ(x,y) = x^{2} + y^{2} - 2r^{2}[/itex] then do the double integral
[itex]∫^{x}_{0}∫^{r}_{-r} x^{2} + y^{2} - 2r^{2} dy dx[/itex]
from that I got an answer of [itex]\frac{2rx^{2}}{3}[/itex]
EDIT: I get [itex]\frac{2rx^{2}}{3} - \frac{10r^3x}{3}[/itex] rather then [itex]\frac{2rx^{2}}{3}[/itex]
Is that correct? Or am I supposed to follow Example 1 on this page, http://tutorial.math.lamar.edu/Classes/CalcIII/LineIntegralsPtI.aspx ?
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