Question

Heat engines take input energy in the form of heat, use some of that energy to do work, and exhaust the remainder. Similarly, a person can be viewed as a heat engine that takes an input of internal energy, uses some of it to do work, and gives off the rest as heat. Suppose a trained athlete can function as a heat engine with an efficiency of 0.10. (a) What is the magnitude of the internal energy that the athlete uses in order to do 1.5x104 J of work? (b) Determine the magnitude of the heat the athlete gives off.

Answer 1

Answer:

a).$Q_{h}=1.5x10^5J$

b).$Q_{c}=13.2x10^3J$

Explanation:

a).

Using the law of thermodynamic and using to isovolumetric

ΔU=Qh

$Q_{h}=\frac{W_{net}}{Efficiency}$

So to determine the internal energy knowing the work it do

$Q_{h}=\frac{1.5x10^4J}{0.10}=1.5x10^5J$

b).

Efficiency is the work done in relation of the work apply in this case to produce heat so:

$E=\frac{Q_{h}-Q_{c}}{Q_{h}}$

Solve to Qc

$Q_{c}=Q_{h}*[1-E]$

$Q_{c}=1.5x10^4J*(1-0.10)$

$Q_{c}=13.2x10^3J$