A brick weighing 4.0 kg is dropped into a 1.0 m

A brick weighing $4.0 \mathrm{~kg}$ is dropped into a $1.0 \mathrm{~m}$ deep river from a height of $2.0 \mathrm{~m}$. Assuming that $80 \%$ of the gravitational potential energy is finally converted into thermal energy, find this thermal energy in calorie.