Mass to energy equivalence question

[eXmag]

Homework Statement

An unknown amount of mass lost from a fusion reaction is converted to energy. Determine the amount of mass equal to 17.6 MeV of energy.

Homework Equations

E=mc2?

The Attempt at a Solution

17.6=m(931.5)
m=0.01889u
Not sure if this is correct

 

[rude man]

Homework Statement

An unknown amount of mass lost from a fusion reaction is converted to energy. Determine the amount of mass equal to 17.6 MeV of energy.

Homework Equations

E=mc2?

The Attempt at a Solution

17.6=m(931.5)
m=0.01889u
Not sure if this is correct

Where did "931.5" come from? √(931.5) = 30.52, I don't recognize this as being c ...

 

[Dick]

Where did "931.5" come from? √(931.5) = 30.52, I don't recognize this as being c ...

931.5 MeV is the rest energy of 1 amu of mass. The 'attempt at a solution' wasn't very well explained. To say the least.

 

[rude man]

931.5 MeV is the rest energy of 1 amu of mass. The 'attempt at a solution' wasn't very well explained. To say the least.

Yeah, so looks like E = mc² is irrelevant & we have just a ratio of energies and finding out how many gm to 1 a.m.u.?

 

[Dick]

Yeah, so looks like E = mc² is irrelevant & we have just a ratio of energies and finding out how many gm to 1 a.m.u.?

The easy way to solve it is to use 1amu*c^2=931.5 MeV (because you've memorized it) and solve it using ratios. That's how the OP got the right answer if u=amu. But the OP butchered the units and I know the OP doesn't know whether it's right or wrong. That's not good. Just using E=mc^2 and paying some attention to units would be much better. It would show understanding. It's hardly irrelevant. I was just pointing out where the 931.5 came from.