Question

A spaceship is moving east at speed 0.82c relative to earth. a second spaceship is moving west at speed 0.82c relative to earth. what is the speed of one spaceship relative to the other spaceship?

Answer 1

Using the velocity addition formula v = (u - w)/(1 - uw) in natural units,

v = (0.82 - (-0.82))/(1-(0.82)(-0.82)) = 0.98 (2 s.f.)

or 0.98c in standard units.