“Test Your Knowledge”
Problem 1: An electron has a kinetic energy of 0.100 MeV. Find its speed according to
classical and relativistic mechanics.
Given:
Find:
A.
Classical Physics
B.
Relativity
Problem 2: In the frame S, two electrons approach each other, each having a
speed u = c/2. What is the relative speed of the two electrons? (Hint: Transform to a
frame where one electron is stationary)
Problem 3: In the frame S, an electron has velocity c/2 in the x-direction and a photon
has a velocity c in the y-direction. What is the relative speed of the electron and the
photon?
y
U2y = c
x
U1x = c/2
Problem 4: A collision between two particles of equal mass as seen by observers in
frames S and S’ is shown below:
y
v
v
x
v
v
After Collision
Before Collision
v’2
y’
x’
v’
Before Collision
(particle 2 at rest)


v’2
After Collision
Show that if linear momentum (as defined in classical physics) is conserved in frame S
then it isn’t conserved in frame S’.