A rigid uniform slab hangs symmetrically from three vertical cables of identical length and cross-sectional area. The outer cables have Young’s modulus E and the central one 3E. Find the percentage of slab weight carried by the central cable.
Symmetry prevents slab rotation, so all cables extend equally. Cable stiffness is EA/L; their stiffnesses are proportional to 1:3:1. The central force is therefore 3/(1+3+1)=3/5 of the weight, or 60%. Equal extension does not mean equal force when moduli differ.
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