Question

By sucking through a straw, a student can reduce the pressure in his lungs to $750\text{mm}$ of $Hg$ (density $=13.6{\text{gm/cm}}^3$). Using the straw, he can drink water from a glass upto a maximum depth of :

• A. $10\text{cm}$
• B. $75\text{cm}$
• C. $13.6\text{cm}$
• D. $1.36\text{cm}$

Answer 1

Answer: (C)

$13.6\text{cm}$

Pressure difference created $=10\text{mm}$ of $Hg$.
This must be equal to the pressure of water column being created in the straw. If height of water column be $h$
$h\rho g=\frac{10}{10}\times 13.6\times g$
$h\times 1=13.6\Rightarrow h=13.6\text{cm}$