Question

The heart of a man pumps $4000cc$ of blood through the arteries per minute at a pressure of 130 mm Hg. If the density of mercury is $13.6\times {10}^{3}kg/m^3$, what is the power of heart? $(g=9.8m/s^2)$

• A. $1.17watt$
  
• B. $2.30watt$
  
• C. $1.15hp$
  
• D. $0.115hp$
  

Answer 1

The correct option is A $1.17watt$

We know that power is equal to rate of doing work. In the given configuration we can consider that given volume of blood has been raised by a certain height, whose equivalent height in terms of mercury is $130mm$, thus power can be equating it to rate of increase of potential energy of the equivalent mercury column (instead of blood column). Thus Power calculation can be done by using the formula, $P=mgh/t$.

Now , here mass of $4000c.c$ of mercury should be calculated, as in equivalent terms , the work done in pushing $4000c.c$ of blood to a certain height is same as the work done in pushing the same volume of mercury to a height of $130mm$.

So, $P=4000\times {10}^{-6}\times 13.6\times {10}^3\times 10\times 0.13/60=1.17watt$