PR Physics question help

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1

<p>The question deals with center of mass:</p>

<p>Three thin, uniform rods each of length L are arranged in the shape of an inverted U. The two rods on the arms of the U each have mass m; the third rod (the top rod) has mass 2m. How far below the midpoint of the horizontal rod is the center of the mass of this assembly. </p>

<p>The answer is L/4, but I keep getting L/2...</p>

<p>Wouldn't you just do y = [[(m)(L)+(m)(L)+(2m)(0)]/(m+m+2m)] and obtain L/2?</p>

2

<p>bumpppppppp</p>

3

<p>At the center of mass, the sum of the torques is equal to 0. Think about that first then work from there</p>

4

<p>draw a picture:</p>

<p>._
|…|</p>

<p>they asked for the height, so that is the y-coordinate:</p>

<p>y=sum(mx)/sum(m)
y=(m<em>L/2+2m</em>0+m*L/2)/4m</p>

<p>y= (mL)/4m = L/4</p>

5

<p>It looks like you found the x-coordinate. Actually you didn’t correctly find the x-coordinate either, but were close.</p>