Question

When a dolphin glides through air, it experiences an external pressure of $0.75\text{m}$ of mercury. The absolute pressure on dolphin when it is $4\text{m}$ below the free surface of the water is
$[\text{Take}g=10{\text{m/s}}^2]$

• A. $150\text{kPa}$
• B. $135\text{kPa}$
• C. $142\text{kPa}$
• D. $40\text{kPa}$

Answer 1

The correct option is C $142\text{kPa}$

Absolute pressure is given by
$P_{\text{abs}}=P_{atm}+P_{\text{gauge}}$

$\Rightarrow P_{\text{atm}}=(\rho gH{)}_{\text{mercury}}=13600\times 10\times 0.75=102000\text{Pa}$
$\Rightarrow P_{\text{gauge}}=(\rho gH{)}_{\text{water}}=1000\times 10\times 4=40000\text{Pa}$
So,
$P_{\text{abs}}=142000\text{Pa}=142\text{kPa}$