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 $g=10m{{s}^{-2}}$).
$\begin{align}
  & \left( A \right)2\times {{10}^{5}}Pa \\
 & \left( B \right)3\times {{10}^{5}}Pa \\
 & \left( C \right)2\times {{10}^{6}}Pa \\
 & \left( D \right)3\times {{10}^{6}}Pa \\
\end{align}$

Answer 1

Hint: As the thighs are the lower part of the body, obviously they have to carry the weight of the whole body. Firstly, calculate the area of the thighs and then force exerted by the body on them and then the pressure produced.

Formula used: $P=\dfrac{F}{A}$
$P$- pressure exerted
$F$- force
$A$- area

Complete step by step answer:
Let us first understand what is meant by pressure.
Pressure on a surface of a body is the force acting perpendicular to surface on unit area of the surface.
Average pressure on a surface is simply the perpendicular force acting on the surface upon the area of the surface.
i.e. $P=\dfrac{F}{A}$.
In the given case, earth will exert a gravitational force on the upper part of the human body. The gravitational force on a body of mass m is given as F = mg, where g is acceleration due to gravity.
The mass of the upper part is 40kg and the value of g = 10$m{{s}^{-2}}$ .
Therefore, $F=mg=(40)(10)=400N$.
Due to this force, the upper part will exert a pressure on the cross section of the femurs.
It is given that the area of the cross section of each thigh is $10c{{m}^{2}}=10{{\left( {{10}^{-2}}m \right)}^{2}}={{10}^{-3}}{{m}^{2}}$.
Hence, the total cross sectional area is $A=2\times {{10}^{-3}}{{m}^{2}}$
Therefore, the average pressure on the thighs is $P=\dfrac{F}{A}=\dfrac{400}{2\times {{10}^{-3}}}=2\times {{10}^{5}}Pa$.

So, the correct answer is “Option A”.

Additional Information: Pressure is defined because the physical force exerted on an object. The force exerted is perpendicular to the surface of objects per unit area. The essential formula for pressure is ${F}/{A}\;$ (Force per unit area). Unit of pressure is Pascals (Pa). sorts of Pressures are Absolute, Atmospheric, Differential, and Gauge Pressure.

Note: Because the hazard isn't weight but body fat, simple height and weight charts have been given thanks to a mathematical formula that uses these two measurements to calculate the body mass index, or BMI. As we could take air pressure under consideration in every calculation, but usually it doesn't end in an outsized net force on objects of interest because it's about equivalent everywhere. You're right that air pressure is robust, though, so when it is not roughly balanced everywhere it can have dramatic effects.