Question

A gas in a closed container is heated with $10J$ of energy, causing the lid of the container to rise $2m$ with $3N$ of force. What is the total change in energy of the system ?

• A. $10J$
• B. $4J$
• C. $-10J$
• D. $-4J$

Answer 1

Answer: (B)

$4J$

Explanation:
For this problem, use the first law of thermodynamics. The change in energy equals the increase in heat energy minus the work done.
$\Delta U=Q-W$
We are not given a value for work, but we can solve for it using the force and distance. Work is the product of force and displacement.
$W=F\Delta x$
$W=3N\times 2m$
$W=6J$
Now that we have the value of work done and the value for heat added, we can solve for the total change in energy.
$\Delta U=Q-W$
$\Delta U=10J-6J$
$\Delta U=4J$