# Homework Help: Energy/Work/Efficiency/Metabolic Rate Question

1. Apr 19, 2007

### miava

1. The problem statement, all variables and given/known data

A friend is doing a work out in a gym.

Suppose the efficiency for the activities in the work out is 10% and the metabolic rate is 700w, how much physical work would she have done in 20 minutes?

3. The attempt at a solution

I have no idea how to start this question! I can't find any related formulas, so I was just hoping someone could help me out and start me in the right direction :-)

2. Apr 19, 2007

### denverdoc

Hi.
Do you know definition of efficiency? Here it means that for every 10 watts she burns only one is going into physical work. A watt is unit of power.

the total work is power*time . You will need to keep your units straight so use seconds. Does that help?

3. Apr 22, 2007

### miava

Ok, so is the 700w per hour?? If so that would mean 70 watts going into work; 1.167 per minute; 23.33w of power for the 20 minutes. Is that correct?