Question

in a heat engine, 500 j of heat enters the system, and the piston does 300 j of work.
what is the final internal (thermal) energy of the system if the initial energy is 1500 j?
200 j
800 j
1300 j
1700 j

Explanation:

Step1: Recall first law of thermodynamics

$\Delta U = Q - W$, where $\Delta U$ is change in internal energy, $Q$ is heat added, $W$ is work done by system.

Step2: Calculate change in internal energy

$Q = 500\ \text{J}$, $W = 300\ \text{J}$
$\Delta U = 500 - 300 = 200\ \text{J}$

Step3: Find final internal energy

Final energy = Initial energy + $\Delta U$
Initial energy = $1500\ \text{J}$
Final energy = $1500 + 200 = 1700\ \text{J}$

Answer:

1700 J