Question

What would be the greatest length of a steel wire, which when fixed at one end can hang freely without breaking (Density of steel = $7800kg/m^3$ and Breaking stress = $7.8 \times 10^8 N/m^2)

• A. 1000 m
• B. 10, 000 m
• C. 7, 000 m
• D. 700 m

Answer 1

The correct option is B 10, 000 m

$Stress=F/A=mg/A=\rho ALg/A=\rho Lg$
Thus, maximum length is $L=Stress/\left(\rho g\right)=(7.8\times {10}^8)/(7800\times 10)={10}^4$
Maximum length that can be used = 10,000 m
The correct option is (b)