Question

A boy can reduce the pressure in his lungs to $750mm$ of mercury. Using a straw he can drink water from a glass upto the maximum depth of (atmospheric pressure = $760mm$ of mercury, density of mercury = $13.6gc{m}^{-3}$)

• A. 13.6 cm
• B. 9.8 cm
• C. 10 cm
• D. 76 cm
• E. 1.36 cm

Answer 1

Answer: (A)

By hydrostatic pressure
$h\rho g=h_w\cdot {\rho }_w\cdot g$
$h_w=\frac{h\cdot \rho }{{\rho }_w}$
$=\frac{10\times 10^{-3}\times 13.6\times 10^3}{1\times 10^3}$
where $h=\left(760\times 10^{-3}-750\times 10^{-3}\right)m$
$h=10\times 10^{-3}m$
$\rho =13.6\times 10^{3}kg/m^3$
${\rho }_w=1\times 10^{3}kg/m^3$
$=136.0\times 10^{-3}$
$=13.6\times 10^{-2}m$
$=13.6cm$