A plutonium- 239 nucleus initially at rest undergoes alpha decay to produce a uranium-235 nucleus. The uranium-235 nucleus has a mass of 3.90 x 10^-25 kg and moves away with a speed of 2.62 x 10^5 m/s. Determine the minimum wage electric potential difference that is required to bring the alpha particles to rest. This question is worth 12 marks and marks are awarded based in the two physics principles u choose from below and your final answer.

Question

A plutonium- 239 nucleus initially at rest undergoes alpha decay to produce a uranium-235 nucleus. The uranium-235 nucleus has a mass of 3.90 x 10^-25 kg and moves away with a speed of 2.62 x 10^5 m/s. Determine the minimum wage electric potential difference that is required to bring the alpha particles to rest. This question is worth 12 marks and marks are awarded based in the two physics principles u choose from below and your final answer.
uniform motion 
accelerated motion
circular motion 
work energy 5heorem 
conservation of momentum 
conservation of mass energy 
conservation of charge
cpnserbation of nucleons 
wave particle duality
I wanted to find the velocity of the alpha particle through conservation of momentum and the. Ek= vq. I dont understand how this could possibly,y be worth 12 marks but also how this uses two physics COncepts! I would really appreciate some feedback on where I went wrong.