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 up to the maximum depth of (atmospheric pressure = 760 mm 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)

13.6 cm

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