Final answer:
The mass of the original body before the explosion is the sum of the rest masses of the two fragments because the total momentum remains zero, making the mass of the original body C. 2.0 kg.
Step-by-step explanation:
The question pertains to the conservation of momentum and energy in the context of a relativistic explosion, where a stationary body explodes into two fragments, each of mass 1.0 kg, that move apart at speeds of 0.6c relative to the original body.
To solve this, we must use the principle of conservation of momentum in relativistic mechanics. The total momentum of the system before the explosion must equal the total momentum of the system after the explosion. Because the original body is stationary, its initial momentum is zero. After the explosion, the two fragments have equal and opposite momenta, since they move at the same speed in opposite directions. This implies that the total momentum after the explosion remains zero (when vector quantities are considered).
To calculate the mass of the original body, we have to consider the relativistic mass increase of the fragments due to their high speeds (0.6c). However, the fact that the total momentum remains zero irrespective of the speed implies that the mass of the original body equals the sum of the rest masses of its two fragments. Therefore, the mass of the original body is just the sum of the rest masses of the two fragments, which is 2.0 kg.