Question

A student does 1,000 J of work when she moves to her dormitory. Her internal energy is decreased by 3,000 J. Determine the heat during this process. Does she gain or lose her heat?

Answer 1

Answer:

-2000 J (heat lost)

Explanation:

We can solve the problem by using the 1st law of thermodynamics:

$\Delta U = Q-W$

where

$\Delta U$ is the change in internal energy of a system

Q is the heat absorbed by the system

W is the work done by the system

In this situation, we have

$W=1000 W$ (work done by the student)

$\Delta U = -3000 J$ (decrease in internal energy)

So the heat is

$Q=\Delta U + W = -3000 J +1000 J = -2000 J$

And the negative sign means the student has lost heat.