What is the correct speed of alpha particles directed towards lead foil?

  • Thread starter Thread starter hayowazzup
  • Start date Start date
  • Tags Tags
    Alpha Speed
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
1 reply · 2K views
hayowazzup
Messages
63
Reaction score
0

Homework Statement


A beam of α particles with energy/particle = 2.86 MeV is directed towards lead foil.
What is the speed of the α particles?

Homework Equations


E = 1/2 mv^2
v = SQRT(2E/m)
v = SQRT((2)(2.86E+6)(1.602E-19) / (1.673E-27) ) = 23403526 m/s = 0.078c
but the ans is 0.039c which is half of the answer above. Why??


The Attempt at a Solution

 
Physics news on Phys.org

Discussion

Did you do your calculations right? Did you use the right constants?

Punching
(2 * 2.86 MeV / (4 * (proton mass)))^(1/2) / c​
into google gives me the correct answer. (I've assumed the difference in proton and neutron masses are negligible)

Incidentally, I'm assuming you are neglecting relativistic effects?