A particle is moving the +x direction at speed c/2.Another particle is moving in the -x direction at speed c/2 toward the first particle.Which of the following best describes the speed of one particle as seen by an observer moving with the other particle?
A)c
B)some value less than 3c/4
C)some value more than 3c/4
D)3c/4

Question

Quizplus · Accepted Answer

According to the theory of relativity, the velocity of one object as seen by another cannot be simply added when the speeds involved are close to the speed of light. The formula for relativistic velocity addition must be used instead. This formula ensures that the resulting speed is less than the speed of light, c, but it will be more than the classical addition of speeds (which would have suggested 3c/4 in this case). Therefore, the speed of one particle as seen by the other will be some value more than 3c/4 but less than c.

A Particle Is Moving the +X Direction at Speed C/2