Question

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

• 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 $
$ =13.6\, cm $