Problem 5PE

Suppose a woman does 500 J of work and 9500 J of heat transfer occurs into the environment 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.) (b) What is her efficiency?

Solution 5PE

(a)

Substitute -9500 J for Q, and 500 J for W solve for internal energy,

ΔU= (-9500J) - 500 J

= -10000 J

the internal energy decreases by 10,000 J.

(b)

Convert efficiency in percentage,

Efficiency = (0.05) (100)

= 5 %

efficiency of women is 5 % .