So I made this problem up to visualize the einstein velocity transformations between inertial frames. 1. The problem statement, all variables and given/known data I throw a frisbee due north. It goes north at a constant velocity of .7c. At the same time I throw it, a bird flies in a straight line at a constant velocity of .5c at such an angle that its northward component is .3c and its eastward component is .4c, relative to the frisbee. It is going toward a birdfeeder located 1 light-minute north and .4 light-minutes east of where I stand. Is the bird really going toward the birdfeeder in both the frisbee's inertial frame and my inertial frame? 2. Relevant equations vx = (vx' + β)/(1+vx'β) vy = (vy'(√1 - β2)/(1-vx'β) Apostrophied velocities are measured in the frisbee's frame, which moves at velocity "beta" relative to my frame. 3. The attempt at a solution In the frisbee's frame, the birdfeeder is heading south at .7c. In one minute, it will be .7 light-minutes south of where it was before. The bird moves relative to the frisbee up .3 light-minutes and east .4 light-minutes, so it should meet the birdfeeder in one minute. In the home frame, The northward component of the bird is .3+.7 / 1+(.3)(.7) = .82645 The eastward component of the bird is .4(sqrt(1-.49))/1+(.3)(.7) = .23608 Since .82645/.23608 does not equal 1/.4, the bird is not heading toward the birdfeeder. I definitely did something wrong to get this contradiction. Would anyone like to try it?