Two electrons move in opposite directions at 0.70c as measured in the laboratory.The speed of one electron as measured from the other is:
A)0.35c
B)0.70c
C)0.94c
D)1.00c
E)1.40c

Question

Quizplus · Accepted Answer

We can use the relativistic velocity addition formula to calculate the speed of one electron as measured from the other:

v' = (v - u)/(1 - uv/c^2)

where v is the velocity of one electron in the lab frame (0.70c), u is the velocity of the other electron as measured from the lab frame (also 0.70c, but in the opposite direction), and c is the speed of light.

Plugging in the values, we get:

v' = (0.70c - (-0.70c))/(1 - (0.70c)(-0.70c)/c^2)
   = 1.40c/(1 + 0.49)
   = 0.94c

Therefore, the speed of one electron as measured from the other is 0.94c, so the best choice is C.

Two Electrons Move in Opposite Directions at 0