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# COM Watch

They found Mx to be (phb2)/3 and then proceeded to use this value in the numerator of the equation for x bar (the x-coordinate of the centre of mass of the lamina). Why have they done this? The equation for Mx is pxy whereas the equation for the x-coordinate is just xy. So why have they substituted Mx (=pxy) into xy ?
2. It's been a while since I've done this, but haven't they just done xbar=(M xbar)/M?
3. (Original post by Hopple)
It's been a while since I've done this, but haven't they just done xbar=(M xbar)/M?
Ah I see. Wouldn't it have been easier to just use the formula for xbar without considering the Mass?

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4. (Original post by GPODT)
Ah I see. Wouldn't it have been easier to just use the formula for xbar without considering the Mass?
The formula for xbar does consider the mass, just in the form of an integral. In this case, it's easier to work out the mass using area (triangles are easy) and the fact that it has uniform density.

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Updated: April 13, 2013
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