Physics
posted by David .
A passenger on a train traveling 90km/h on a straight, level track notes that it takes another train (180 m long and moving with constant velocity) 4.0s to pass by. What is the velocity of that passing train relative to the ground?
**please include explanation** thnx!!

The relative velocity is the distance divided by the time.
Now subtract the train moving 90km/hr, and you have the other train velocity.
Watch units. 
so:
V = 180 m / 4 s = 45 m/s
convert to km/h
V = 162 km/h
This is the velocity relative to the first train, which is moving 90 km/h relative to the ground.
Then V = 162 + 90 km/h = 252 km/h
That's pretty fast...:P