[填空题]
(a) What mass of $_{92}^{235}\text{U}$ was actually fissioned in the first atomic bomb, whose energy was the equivalent of about 20 kilotons of TNT (1 kiloton of TNT releases $5 \times 10^{12}\ \text{J}$)? $\approx $ $\ \text{kg}$
(b) What was the actual mass transformed to energy?$\approx $ $\ \text{g}$
