Does an Atomic Bomb's Explosion in a Contained Box Affect Its Weight?

[bwilhelm]

Homework Statement

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

Homework Equations

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?

 

[Dick]

Yes. Think about it. Suppose we a had a process that could completely convert mass to photons and back again. Now we put it in your box. It has weight w1. Now convert the mass to photons. If it now has weight w2<w1, then we could push it up some distance, convert the photons back into mass and move the heavier box back down. Since we did less work pushing the box up then we got by letting it back down we would have a perpetual motion machine.

 

[m2003]

I would approach this problem by first considering the basic principles of physics. The atomic bomb is a form of nuclear energy, which is released through the process of nuclear fission or fusion. In this process, a small amount of mass is converted into a large amount of energy, as described by Einstein's famous equation E=mc^2. This means that the mass of the bomb and the box would decrease after the explosion, as some of the mass is converted into energy.

However, it is important to note that the energy released would still have a mass component. Photons, which are particles of light, do have a small amount of mass according to the theory of relativity. Therefore, the weight of the box would decrease, but not by the full amount of the bomb's mass. The weight would still decrease, but not to zero.

Additionally, the explosion would also produce heat and sound, both of which have mass as well. This would also contribute to the decrease in weight of the box. So, the correct answer to the question would be b) less than before, but not by the full amount of the bomb's mass.

It is also important to note that the weight of the box may also be affected by external factors, such as air resistance and gravity. These factors would need to be taken into consideration when calculating the weight of the box after the explosion.

In conclusion, the weight of the box would decrease after the explosion of an atomic bomb, but not by the full amount of the bomb's mass. The decrease in weight would be due to the conversion of mass into energy, as well as the mass of the energy released.