- #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. x

_{f }= x

_{i }+ ViΔt + 1/2a

_{x}(Δt)

^{2}

2. a

^{2}= b

^{2}+ c

^{2}

## The Attempt at a Solution

I used the first equation to calculate the velocity of the ball in the y-axis. I assumed that x

_{i}= a

_{x}= 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?