Thermodynamics Question 3
Question 3 - 2024 (27 Jan Shift 1)
$0.08 \mathrm{~kg}$ air is heated at constant volume through $5^{\circ} \mathrm{C}$. The specific heat of air at constant volume is
$0.17 \mathrm{kcal} / \mathrm{kg}^{\circ} \mathrm{C}$ and $\mathrm{J}=4.18$ joule $/ \mathrm{cal}$. The change in its internal energy is approximately.
(1) $318 \mathrm{~J}$
(2) $298 \mathrm{~J}$
(3) $284 \mathrm{~J}$
(4) $142 \mathrm{~J}$
Show Answer
Answer: (3)
Solution:
$\mathrm{Q}=\Delta \mathrm{U}$ as work done is zero [constant volume]
$\Delta \mathrm{U}=\mathrm{ms} \Delta \mathrm{T}$
$=0.08 \times(170 \times 4.18) \times 5$
$\simeq 284 \mathrm{~J}$
