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# stupid phy6 question, calculation question help. watch

1. January 2003 - phy6
question
2 (iii) Calculate the kinetic energy of the pair of α -particles in joules,

there some data like mass of li, proton and alpha particle. The paper is on the taggart site.
2. Do you have a link to the question?
3. I just did that yesturday.
First find the mass defect from e=mc^2.
This is from the nuclear equation.

Mass before = 8.02165kg
Mass after = 8.003kg
mass defect = 0.01865kg

I then got it all wrong!
I dont understand why they times by the mass of an electron?
4. (Original post by SinghFello)

Mass before = 8.02165kg
Mass after = 8.003kg
mass defect = 0.01865kg

I then got it all wrong!
I dont understand why they times by the mass of an electron?
Well, I think the unit is u not kg
And they times mass of 1 u, not mass of 1 e
5. i did this in particle physics, you have to find the difference in u then convert to kilograms [this is where particle physics is good]

but how the *** did they get that difference in mass?

i thought it would be either
proton + li - [2 alphas]
or
proton - [2 alphas]

i dunno how they did it
6. ah i done it!

i got alpha mass n proton mass mixed up lol

so you do this
mass before = li + proton [in u]
mass after = 2 x alhpa mass

e=mc^2
as e = joules
mass needs to be in kgs, so convert with 1.66 x10^-27kg = 1u

phew
7. (Original post by nas7232)
how did you get Mass after = 8.003kg
He just times 2 mass of alpha particle
m = 2 * 4.00150 u = 8.003u
8. (Original post by nas7232)
i did this in particle physics, you have to find the difference in u then convert to kilograms [this is where particle physics is good]

but how the *** did they get that difference in mass?

i thought it would be either
proton + li - [2 alphas]
or
proton - [2 alphas]

i dunno how they did it
That's how they did do it:
(H + Li) - 2He

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