In Problem 236, how should the lengths of the two identical copper rods be changed so that each material will be stressed to its allowable limit?
$\left( \dfrac{\sigma L}{E} \right)_{co} = \left( \dfrac{\sigma L}{E} \right)_{st}$
$\dfrac{70 L_{co}}{120\,000} = \dfrac{140(240)}{200\,000}$
$L_{co} = 288 \, \text{ mm }$ answer
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