- #1
MickeyBlue
- 26
- 2
Homework Statement
A train is traveling 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.
Homework Equations
1. xf = xi + ViΔt + 1/2ax(Δt)2
2. a2 = b2 + c2
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?