Question

The two thigh bones, each of cross-sectional area $10 \,cm ^2$ support the upper part of a human body of mass $40\, kg$. Estimate the average pressure sustained by the bones. Take $g=10 \,m / s ^2$

• A. $2 \times 10^5 \,N / m ^2$
• B. $5 \times 10^4\, N / m ^2$
• C. $2 \times 10^7\, N / m ^2$
• D. $3 \times 10^6 \,N / m ^2$

Answer 1

Answer: (A)

Total cross-sectional area of the thigh bones
$A=2\left(10 \times 10^{-4}\right)=2 \times 10^{-3} m ^2$
Force acting on the bones $=m g=40 \times 10=400\, N$
$\therefore P_{ av }=\frac{F}{A}=\frac{400}{2 \times 10^{-3}}=2 \times 10^5 \, N / m ^2$