Question

Two thigh bones (femurs) of $10 \ cm^2$ area support a 40 kg body. Average pressure is:

• A. $3.0 \times 10^5 \ N/m^2$
• B. $2.0 \times 10^5 \ N/m^2$
• C. $1.0 \times 10^5 \ N/m^2$
• D. $2.0 \times 10^4 \ N/m^2$

Hint:

Pressure is force per unit area. For distributed loads, sum areas if multiple supports are involved.

Answer 1

The Correct Option is B

The total force due to weight is:
\[ F = mg = 40 \times 9.8 = 392 \text{ N} \]
The total cross-sectional area is:
\[ A = 2 \times 10 \times 10^{-4} = 2 \times 10^{-3} \text{ m}^2 \]
The pressure is:
\[ P = \frac{F}{A} = \frac{392}{2 \times 10^{-3}} \approx 2.0 \times 10^5 \text{ N/m}^2 \]