Physics Thermodynamics NUMS 2020
PMDC Verified Question 47 of 54
In a certain process, 400J of heat energy is supplied to a system and at the same time 150J of work is done by the system. The increase in internal energy of system is
A
150J
B
500J
C
300J
D
250J
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 250J
1. Concept:

The First Law of Thermodynamics dictates that energy is conserved. The heat added to a system splits into changing its internal energy and doing work on the surroundings.

2. Formula:

$$Q = \Delta U + W$$

3. Solution:

  • Identify given values with correct sign conventions: Heat supplied \(Q = +400 \text{ J}\), Work done BY the system \(W = +150 \text{ J}\).


  • Rearrange the formula to solve for internal energy: \(\Delta U = Q - W\).


  • Substitute values: \(\Delta U = 400 - 150\).


  • Result: \(\Delta U = 250 \text{ J}\).


4. Why other options are incorrect:

Adding the numbers instead of subtracting gives 550J. Failing to account for work gives 400J. The correct energy balance requires subtracting the energy lost as work.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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