When ${ }_{92} U^{235}$ undergoes fission, 0.1% of its original mass is changed into energy. How much energy is released if 1 kg of ${ }_{92} U^{235}$ undergoes fission

$9 \times 10^{13} \mathrm{~J}$

$E=\Delta m c^2, \Delta m=\frac{0.1}{100}=10^{-3} \mathrm{~kg}$

∴  $E=10^{-3} \times\left(3 \times 10^8\right)^2=10^{-3} \times 9 \times 10^{16}=9 \times 10^{13} \mathrm{~J}$