Answer to Question #259441 in Mechanics | Relativity for Karthi

Question #259441

Q1. For the shaded area shown in figure. Determine:-Co-ordinates of centroid



The removed area is semi-circle and all the given dimensions are in cm. Dimension of rectangle is 12.5*20 cm² and diameter of semi-circle is 7.5 cm.



12.5



7.5

1
Expert's answer
2021-11-01T12:54:24-0400


Since figure is symmetric respect to vertical axis:

xC=20/2=10x_C=20/2=10


yC=Sx/Ay_C=S_x/A

where Sx is static moments around x axis,

A is area of figure


Sx=SxiS_x=\sum S_{x_i}


Sxi=AiyCiS_{x_i}=A_i y_{C_i}

where Ai are subarea,

yci is centroid coordinate of subarea


for rectangle:

A1=2012.5=250A_1=20\cdot 12.5=250 cm2

yc1=12.5/2=6.25y_{c1}=12.5/2=6.25


for semi-circle:

A2=πR2/2=3.752π/2=22A_2=\pi R^2/2=3.75^2\pi/2=22 cm2

yc2=12.54R/(3π)=12.543.75/(3π)=10.9y_{c2}=12.5-4R/(3\pi)=12.5-4\cdot 3.75/(3\pi)=10.9


A=A1A2=25022=228A=A_1-A_2=250-22=228 cm2


Sx=A1yc1A2yc2=2506.252210.9=1322.7S_x=A_1y_{c1}-A_2y_{c2}=250\cdot6.25-22\cdot10.9=1322.7


yC=1322.7228=5.8y_C=\frac{1322.7}{228}=5.8



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