Density of water at \( 4^\circ \text{C} \) and \( 20^\circ \text{C} \) are \( 1000 \, \text{kg/m}^3 \) and \( 998 \, \text{kg/m}^3 \) respectively. The increase in internal energy of \( 4 \, \text{kg} \) of water when it is heated from \( 4^\circ \text{C} \) to \( 20^\circ \text{C} \) is _____ \( \text{J} \).
(Specific heat capacity of water \( = 4.2 \, \text{J/kg} \) and \( 1 \) atmospheric pressure \( = 10^5 \, \text{Pa} \))
