Question

an observer sees two spaceships flying apart with speed .99c. What is the speed of one spaceship as viewed by the other

Answer 1

V2 = (V1 - u) / (1 - V1 u / c^2)

V1 = speed of ship in observer frame = .99 c to right

u = speed of frame 2 = -.99 c to left relative to observer

V2 = speed of V1 relative to V2

V2 = (.99 - (-.99 ) / (1 - .99 (-.99)) c

V2 = 1.98 / (1 + .99^2) c = .99995 c