Q. The human heart discharges 75 cc of blood through the arteries at each beat against an average pressure of 10 cm of mercury. Assuming that the pulse frequency is 72 per minute the rate of working of heart in watt, is (Density of mercury =13.6 g/cc and $g = 9.8\ ms^{- 2}$)
A) 11.9
B) 1.19
C) 0.119
D) 119
Explanation
(b) $P = \frac{dW}{dt} = P\frac{dv}{dt}$
$P = h\ d\ g = 10 \times 13.6 \times 980$
$= 1.3328 \times 10^{5}\ dyne/cm^{2}$
$\frac{dv}{dt} =$ Pulse frequency $\times$ blood discharged per pulse
$\frac{dv}{dt} = \frac{72}{60} \times 75 = 90$ cc/sec
$\therefore\ \ $Power of heart $= 1.3328\ \times 10^{5} \times 90$ erg/sec
$= \ 1.19\ W$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.