Understanding the Equation E=mc^2 and Its Applications

[jsmith613]

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

 

[Steely Dan]

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

 

[jsmith613]

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?

 

[Andrew Mason]

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

 

[jsmith613]

thanks