Step 1: Divide the lamina into three rectangular sections and determine their dimensions, areas, and individual centroid coordinates relative to point O (the origin).
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Rectangle 1 (Left):
- Width (w1) = 200 mm
- Height (h1) = 400 mm
- Area (A1) = w1×h1=200mm×400mm=80000mm2
- Centroid x1=2w1=2200=100 mm
- Centroid y1=2h1=2400=200 mm
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Rectangle 2 (Middle):
- Width (w2) = 250 mm
- Height (h2) = 90 mm
- Area (A2) = w2×h2=250mm×90mm=22500mm2
- Centroid x2=w1+2w2=200+2250=200+125=325 mm
- Centroid y2=2h2=290=45 mm
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Rectangle 3 (Right):
- Width (w3) = 300 mm
- Height (h3) = 220 mm
- Area (A3) = w3×h3=300mm×220mm=66000mm2
- Centroid x3=w1+w2+2w3=200+250+2300=450+150=600 mm
- Centroid y3=2h3=2220=110 mm
Step 2: Calculate the total area of the lamina.
Atotal=A1+A2+A3
Atotal=80000mm2+22500mm2+66000mm2=168500mm2
Step 3: Calculate the sum of the moments of the areas about the y-axis (for xˉ).
∑Aixi=A1x1+A2x2+A3x3
∑Aixi=(80000mm2×100mm)+(22500mm2×325mm)+(66000mm2×600mm)
∑Aixi=8000000mm3+7312500mm3+39600000mm3=54912500mm3
Step 4: Calculate the sum of the moments of the areas about the x-axis (for yˉ).
∑Aiyi=A1y1+A2y2+A3y3
∑Aiyi=(80000mm2×200mm)+(22500mm2×45mm)+(66000mm2×110mm)
∑Aiyi=16000000mm3+1012500mm3+7260000mm3=24272500mm3
Step 5: Calculate the coordinates of the centroid (xˉ,yˉ) from point O.
xˉ=Atotal∑Aixi=168500mm254912500mm3≈325.89 mm
yˉ=Atotal∑Aiyi=168500mm224272500mm3≈144.05 mm
The position of the centroid from MO (which is the y-axis) is given by its coordinates (xˉ,yˉ).
The position of the centroid is (∗325.89mm,144.05mm∗).
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