# Power consumption of a human running

arkturus

## Homework Statement

If a 70kg man is running 3 m/s horizontally, how many watts is he consuming?

## Homework Equations

W = N-m/s
N = mass*acceleration

## The Attempt at a Solution

I would assume that in order to get the force in N one would use the gravitational constant of the Earth, but the man is moving in a horizontal line. Regardless, he is technically using work to move 'up' since his center of mass is going slightly up and down. How do I account for this, however?

Thank you.

Staff Emeritus
I would assume that in order to get the force in N one would use the gravitational constant of the Earth, but the man is moving in a horizontal line. Regardless, he is technically using work to move 'up' since his center of mass is going slightly up and down. How do I account for this, however?
Unless you were given typical data for the energy (or force) demanded of a runner I don't think you are going to be able to answer this. Sure, he does lift his CoM during each step, but that energy is returned when he allows it to then fall, so no nett energy expenditure there.

I vaguely recall this same or a similar question from some months back, but I may be imagining things. https://www.physicsforums.com/images/icons/icon6.gif [Broken]

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Homework Helper
Gold Member
What he said. You do not have enough information to calculate the power.

If it was 3m/s vertically that would be a different matter. In that case the man is gaining Potential Energy at a known rate so you could calculate his minimum power output.

If the problem is homework or from a book perhaps type it in word for word?