Question

The two thigh bones (femurs), each of cross-sectional area $10c{m}^2$ support the upper part of a human body of mass $40kg$. Estimate the total pressure sustained by the both femurs. (Given $g=10m{s}^{-2}$).

• A. $2\times {10}^5$ Pa
• B. $3\times {10}^5$ Pa
• C. $2\times {10}^6$ Pa
• D. $3\times {10}^6$ Pa

Answer 1

Answer: (A)

$2\times {10}^5$ Pa

Given, mass of body, $m=40kg;g=10m{s}^{-2}$;
area, $A=2\times$ area of each thigh bone
$=2\times 10c{m}^2=20\times {10}^{-4}{m}^2$
(weight of the body is supported by two thigh bones)
Force, $F=$ weight of the body $=mg=40\times 10$
$=400N$
Pressure, $P=\frac{Force}{Area}=\frac{F}{A}=\frac{400}{20\times {10}^{-4}}$
$=2\times {10}^5$Pa