Question

Suppose a woman does 463 J of work and dissipates 8,854 J of heat in the process. (a) What is the decrease in her internal energy, assuming no change in temperature or consumption of food? (That is, there is no other energy transfer.) kcal (b) What is her efficiency? %

Answer 1

Answer:

Part a)

decrease in internal energy is 2.23 k Cal

Part b)

Efficiency will be 4.9 %

Explanation:

Part A)

As per first law of thermodynamics we know that

$Q = W + \Delta U$

here we have

Q = -8854 J

W = 463 J

now we have

$-8854 J = 463 J + \Delta U$

so we have

$\Delta U = -9317 J = - 2.23 kCal$

So decrease in internal energy is 2.23 k Cal

Part B)

Efficiency of the woman is given as

$\eta = \frac{W}{\Delta U}$

here we have

$\eta = \frac{463}{9317} = 0.049$

So efficiency will be 4.9 %