$100 \mathrm{~g}$ of water is heated from $30^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$. Ignoring the…

$100 \mathrm{~g}$ of water is heated from $30^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$. Ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is $4148 \mathrm{~J} / \mathrm{kg} / \mathrm{K}$ ):
  1. $8.4 \mathrm{~kJ}$
  2. $84 \mathrm{~kJ}$
  3. $2.1 \mathrm{~kJ}$
  4. $4.2 \mathrm{~kJ}$

Solution

$\Delta \mathrm{Q}=\Delta \mathrm{U}+\Delta \mathrm{W}$ (ignoring expansion) $\Delta \mathrm{U}=\mathrm{ms} \Delta \mathrm{T}=0.1 \times 4.184 \times 20=8.368 \mathrm{~kJ}$

Asked in: JEE Main 2011

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