Center of Gravity, Centroid (Composite Body)

Example: Find the y and z coordinates of the composite section shown below.

Strategy: Subdivide this composite section into three rectangular areas each having dimensions b by h as shown below. The moment of the sum of the areas times the

centroid must equal the sum of the moments for each part.

y- centroid: Σ A_i y_cg = ΣA_iy_i (3bh) y_cg = (bh)(h/2) + (bh)(h/2) + (bh)(h + b/2)

y_cg = c = [h + h + (h+b/2)] / 3 = (5h + b)/6 (result)

z-centroid: By symmetry z_cg = 0.

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