# Kinetic energy alpha particle

1. Dec 25, 2013

### astri_lfc

1. The problem statement, all variables and given/known data

could you help me for the question b?

2. Relevant equations
E = mc^2

3. The attempt at a solution

the mass of the alpha particle is 0.66466 x 10^-26 kg >> 4.022 u

put it into the equation, so
E = 4.022 x c x c = 3.615 x 10^17 eV >> 0.0579 joule

which one is true? can you show me where's my wrong?

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Last edited: Dec 25, 2013
2. Dec 25, 2013

### Curious3141

Merry Xmas.

What you're calculating is the energy due to the (rest) mass of the alpha particle. That's not kinetic energy.

The alpha particle's total energy comprises energy due to its (rest) mass plus its kinetic energy. You need to determine the latter.

You can just work with mass, because mass and energy are basically equivalent (or proportional, depending on choice of units). Calculate the total mass of on the left hand side. Calculate the total mass on the right hand side. You may ignore the photon because at the minimum KE of the alpha particle, the photon will have no energy. Can you now figure out the "extra" mass on the LHS? Convert that to energy.

3. Dec 25, 2013

### astri_lfc

merry christmas too ;)

thankyou :D i understand it now!