The internal energy of an ideal gas follows the equation $\mathrm{U}=3.5 \mathrm{PV}+\mathrm{k}$, where k is a constant. The gas expands from an initial volume of $0.25 \mathrm{m}^{3}$ to a final volume of $0.86 \mathrm{m}^{3}$. If the initial pressure is $5 \mathrm{N} \mathrm{m}^{-2}$, the change in internal energy (in joules) is (given $\mathrm{PV}^{1.3}=$ constant) ____ .
Answer
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