Question

If the atmosphere pressure is $76cm$ of mercury, at what depth of water the pressure will becomes $4$ atmospheres?

• A. $31m$
• B. $21m$
• C. $11m$
• D. $9$

Answer 1

The correct option is A $31m$

Given,

$76cm$, Mercury pressure is equal to $1atm$.

Atmospheric pressure, $P_o=1atm=1.013\times {10}^{5}Pa$

Total pressure at depth $h$ is equal to $P$= Pressure due to water + Pressure on surface of water.

Pressure at depth $h$ from surface of water.

$P-P_o={\rho }_{w}gh$

$h=\frac{P-P_o}{{\rho }_{w}g}=\frac{(4-1)\times {1.013\times 10}^5}{1000\times 9.8}=31m$

Hence, depth in water is $31m$