The heart of man pumps 5 litres of blood through the arteries per minute at a pressure of $$150\,mm$$  of mercury. If the density of mercury be $$13.6 \times {10^3}kg/{m^3}$$    and $$g = 10\,m/{s^2}$$   then the power of heart in watt is :

Solution :
$$\eqalign{ & {\text{Power}}\,\vec F \cdot \vec V = PA\vec V = \rho ghAV\,\,\left[ {\because P = \frac{F}{A}\,{\text{and}}\,P = \rho gh} \right] \cr & = \frac{{13.6 \times {{10}^3} \times 10 \times 150 \times {{10}^{ - 3}} \times 0.5 \times {{10}^{ - 3}}}}{{60}} \cr & = \frac{{102}}{{60}} = 1.70\,watt \cr} $$