1. The problem statement, all variables and given/known data A train is travelling east along a straight run of track at 72.0 km/hr. Inside, two siblings 1.9 m apart are playing catch directly across the aisle. The kid wearing a P.J.Harvey T-shirt throws the ball horizontally north. The ball crosses the train and is caught 0.75 s later by her little brother. (Ignore any effects of gravity or friction.) Find the magnitude of the ball's velocity from the little brother's point of view. 2. Relevant equations 1. xf = xi + ViΔt + 1/2ax(Δt)2 2. a2 = b2 + c2 3. The attempt at a solution I used the first equation to calculate the velocity of the ball in the y-axis. I assumed that xi = ax = 0 and got 2.5 m/s. I then used Pythagoras and head-to-tail vector addition to get the actual speed and direction of the ball, taking speed in the x-axis as the speed of the train (20m/s). I took the brother to be moving at the same speed and direction as the train. My final answer was 40 m/s. I know this is the wrong answer but I can't work out why. Any advice?