Calculating Kinetic Energy of an Alpha Particle

[astri_lfc]

Homework Statement

could you help me for the question b?

Homework Equations

E = mc^2

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

my answer is that, but my teacher answer is 1.89x10^-13 joule..

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

 

[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.

 

[astri_lfc]

merry christmas too ;)

thankyou :D i understand it now!