Question:easy
A system does 394 J of work on surrounding by absorbing 701 J heat. What is the change in internal energy of the system?
A system does 394 J of work on surrounding by absorbing 701 J heat. What is the change in internal energy of the system?
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Keep a simple arithmetic check in mind: when a system takes in energy as heat ($+701$) and releases energy by performing mechanical work ($-394$), the net change must simply be the subtraction of the two magnitudes ($701 - 394 = 307$).
Updated On: Jun 12, 2026
- 547 J
- 1095 J
- 307 J
- 394 J
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Recall the first law.
$\Delta U = q + W$, with heat in and work on the system taken as positive.
Step 2: Read the heat term.
The system absorbs 701 J, so heat enters: $q = +701$ J.
Step 3: Read the work term.
The system does 394 J of work on the surroundings, so energy leaves as work: $W = -394$ J.
Step 4: Substitute the values.
$\Delta U = 701 + (-394)$.
Step 5: Compute.
$\Delta U = 701 - 394 = 307$ J.
Step 6: Interpret and choose.
The positive value means internal energy rose by 307 J, matching option (3).
\[ \boxed{\Delta U = 307 \text{ J}} \]
$\Delta U = q + W$, with heat in and work on the system taken as positive.
Step 2: Read the heat term.
The system absorbs 701 J, so heat enters: $q = +701$ J.
Step 3: Read the work term.
The system does 394 J of work on the surroundings, so energy leaves as work: $W = -394$ J.
Step 4: Substitute the values.
$\Delta U = 701 + (-394)$.
Step 5: Compute.
$\Delta U = 701 - 394 = 307$ J.
Step 6: Interpret and choose.
The positive value means internal energy rose by 307 J, matching option (3).
\[ \boxed{\Delta U = 307 \text{ J}} \]
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