Two electrons are ejected in opposite directions from atoms in a sample of radioactive material.Each electron has a speed,as measured by a laboratory observer,of 0.6c.What is the speed of one electron as seen from the other electron?
A)0.361c
B)0.882c
C)1.87c
D)zero
E)1.24c

Question

Quizplus · Accepted Answer

According to the relativistic velocity addition formula, the velocity of one electron as seen from the other electron is:
v' = (v - u) / (1 - uv/c^2)
where v is the speed of one electron relative to the laboratory, u is the speed of the other electron relative to the laboratory, and c is the speed of light. 
Since the electrons are ejected in opposite directions, their relative speed in the laboratory frame is 2v = 1.2c. Thus, we have:
v' = (0.6c + (-0.6c)) / (1 - (0.6c)(-0.6c)/c^2) 
v' = 1.2c / (1 + 0.36)
v' = 0.882c
Therefore, the speed of one electron as seen from the other electron is 0.882c, which corresponds to choice B.

Two Electrons Are Ejected in Opposite Directions from Atoms in a Sample