Superman and Supergirl were playing catch. When Superman is moving with a speed of 0.800c relative to Supergirl, he threw a ball to Supergirl with a speed of 0.600c relative to him.
a. What was the speed of the ball as measured by Supergirl?
I tried to solve number 1. heres my approach. let s be the supergirl frame of reference while s' be the frame of reference by superman, heres my diagram
(<--)superman (--->)ball supergirl(stay)
so s' is going to the left, so it has negative velocity (-0.8c). vx' is going to the right (+0.6c) . now (vx) velocity of ball with respect to supergirl is (-.13c)
using lorentz transformation, vx is negative, so it means its going to the left and it will never reach supergirl. so it appears that answer for letter a is, its impossible?