1. The problem statement, all variables and given/known data I am having some trouble with this one, Suppose an atomic bomb was exploded in a box that was strong enough to contain all the energy released by the bomb. After the explosion the box would weigh: a) more than before the explosion b) less than before c) no change 2. Relevant equations 3. The attempt at a solution My first thought was that the weight of the box would decrease due to the loss of mass when it was converted to energy. But is the mass converted to photons? Photons in motion would contain mass right? And if the box was able to contain everything wouldn't the weight remain the same?