1. The problem statement, all variables and given/known data A passenger in a train moving at 30m/s passes a person standing on a station platform at t= t' =0. Twenty seconds after the train passes, the person on the platform determins that a bird flying along the tracks in the same direction as the train is 800m away. Five seconds later, the bird is 850m away. Assume a constant velocity for all involved. Find the velocity of the bird as determined by the observer on the platform and train passenger. 2. Relevant equations x' = x-vt ----- v is the difference of the velocity between bird and train, t is the same for passenger or person on platform, x is the location of the bird in the frame of the person standing on the platform so(x2 = 850 and x1 = 800) v'=(x2'-x1')/(t2'-t1') 3. The attempt at a solution So what I did is just plugged in the information they gave us so that x1' = 800 - 20m/s(difference between train and bird)*20s and x2' = 850 - 20*25 lastly I found velocity by v'=(x2'-x1')/(t2'-t1') and got -10m/s as my answer. The negative portion seems logically right since the passenger in the train will see the bird come closer and closer as if the bird's velocity is the opposite. I'm just not sure if everything is mathematically correct and was wondering if someone can do a check for me? Thanks alot!