Question

The thigh bones(femurs),each of cross-sectional area $10c{m}^2$ support the upper part of the human body of mass 40 kg.Average pressure sustained by the femurs is:

• A. ${10}^{3}N/m^2$
• B. $2\times {10}^{5}N{m}^{-2}$
• C. $6\times {10}^{-5}N{m}^{-2}$
• D. ${10}^{-3}N{m}^{-2}$

Answer 1

The correct option is B $2\times {10}^{5}N{m}^{-2}$

Area of 1 bone $A_1=10c{m}^2$

Total area $A=2A_1=20c{m}^2=20\times {10}^{-4}{m}^2$

Pressure $P=\frac{Force}{Area}$

Force $F=mg=40\times 10=400N$

$\therefore$ Pressure $P=\frac{400}{20\times {10}^{-4}}=2\times {10}^{5}N{m}^{-2}$