How Much Work Does the Human Heart Perform in a Day?

[Ogakor]

Homework Statement

The human heart is a powerful and extremely reliable pump. Each day, it takes in and discharges about 7,500 liters or blood. If the work done by the heart is that of an average American female, 1.63m; and if the density of blood is 1.03 x 10³ kg/cubic meter,
a) How much work does the heart do in a day?
b) What is its power output in watts and its horsepower?

given:
vol = 7,500 liters x (1000ml / 1 liter) x (1cubic meter / 1 liter) = 7,500,000 cubic meter
h = 1.63 m
p = 1.03 x 10³ kg/cubic meter
t = 24 hourse = 86,400 s

a. So, in solving for work, my friend and I were arguing on what formula to use. He said, we should use W = mgh (potential energy) since everything is given. I said, we should use W = 1/2mv² (kinetic energy). velocity can be solved with height / time. I wanted to use kinetic energy because this is moving energy. Both giving different results.
So, what should we use, the formula for kinetic energy or potential energy?

b. obviously, when work is solved, just use P = W/t and convert it to horse power. Am I correct? I only want to verify, please answer.

 

[Ogakor]

anyone??