[ilovemath]

Look at the attached Q:

I would have said A but this is wrong - 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

[bssjonny]

A is wrong. The energy of a proton cannot be calculated from E = mc^2 however, the energy equivalence of the MASS of a proton can be calculated using the formula.
For B, burning fuel does not actually change the mass of what you have. You have just reacted fuel with O2, if you were to add up the mass of fuel burned with the oxygen used for combustion and the mass of the products formed you would see that the total mass of products and reactants is equal. So E = mc^2 will not work for that.
For D, two protons colliding transfers kinetic energy, however unless there is a mass loss/gain you cannot use the formula either.

The answer must be C. As you may know from the text book, when a matter and antimatter particle collide, they annhilate. (destroy eachother and no longer exist basically). The reason E = MC^2 for this works is because at the start you had the mass of the two particles and then at the end they had anhilated and so their mass was zero. Since there mass had changed, you can sub m into the formula.

[mahnoorbloch]

Dear for this question i wanna help you. The Equation E=mc square is the equation which deals with the relation of mass and energy i.e if certain amount of mass will consume to how much energy will be produced. You ans was wrong which was a. the ans is c.

[mahnoorbloch]

Dear for this question i wanna help you. The Equation E=mc square is the equation which deals with the relation of mass and energy i.e if certain amount of mass will consume to how much energy will be produced. You ans was wrong which was a. the ans is c. because electron and positron will when react they will disappear to give certain amount of energy which will exactly equal to E= mc square.
for further help you can also check this http://www.notes4all.com/Nuclear.Physics.P1.htm

[ilovemath]

thanks all