Homework Help: Some help needed

1. Nov 3, 2004

nazarip

While running, a person dissipates about 0.554 J of mechanical energy per step per kilogram of body mass. If a 62.5 kg runner dissipates a power of 65.4 W during a race, how fast is the person running? Assume a running step is 1.50 m in length.

Well I know that the person loses 34.6 J of mech energy every 1.5 m and loses a total of 65.4 watts during the entire race. Now 65.4 W is just 65.4 J/s, so how can I further relate all of these givens? I am a little confused. Thanks for any help in advance.

2. Nov 3, 2004

maverick280857

In one step, the amount of energy dissipated is given by

$$(62.5kg)(0.554Jkg^{-1})$$ (per step or per 1.50m)

Suppose there are n steps. This corresponds to a distance 1.50n meters. Hence in n steps the energy dissipated per unit time is

$$(62.5)(0.554)(n) = 65.4$$

from this you can get the number of steps he covers in unit time. Multiply it by 1.50m to get the speed. Is this okay?

cheers
vivek

3. Nov 3, 2004

nazarip

Thanks for the help.