Understanding the Equation E=mc^2 and Its Applications

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The discussion revolves around understanding the equation E=mc^2 and its application in a homework problem. The user initially selected option A but later realized it was incorrect, as it failed to account for the kinetic energy of a proton separate from its rest-mass energy. The correct answer is C, which the user seeks to understand better, while options B and D are deemed incorrect due to insufficient information to determine mass or energy solely from rest masses. The conversation emphasizes the importance of additional context, such as velocity, in applying the equation accurately. Overall, the thread highlights common misconceptions in interpreting E=mc^2 in practical scenarios.
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Homework Statement


see attached question


Homework Equations





The Attempt at a Solution



I chose A but this is wrong :S - why?

The answer is C but I cannot see why B/D are wrong.
I literally guess A as this was the only time I had used the fomula
 

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A is wrong because, for example, a proton can have kinetic energy separate from its rest-mass energy.
 
Steely Dan said:
A is wrong because, for example, a proton can have kinetic energy separate from its rest-mass energy.

so why is C correct and B/D wrong?
 
jsmith613 said:
so why is C correct and B/D wrong?
First of all, I think A is wrong because there is no change in mass. B is wrong because you cannot determine the original mass of coal from just the rest mass of a proton and rest mass of an electron. You would have to have other information. Similarly with D you would cannot determine the energy from the rest masses of a proton or electron. You would have to know how fast the protons were moving before collision.

AM
 
thanks
 

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