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Average Velocity

  1. Jan 14, 2010 #1
    1. The problem statement, all variables and given/known data
    Two trains, each having a speed of 34 km/h, are headed at each other on the same straight track. A bird that can fly 60 km/h flies off the front of one train when they are 51 km apart and heads directly for the other train. On reaching the other train it flies directly back to the first train, and so forth. (We have no idea why a bird would behave in this way.) What is the total distance the bird travels before the trains collide?

    2. Relevant equations
    average speed=deltax/deltat

    3. The attempt at a solution
    I'm having alot of trouble even just setting the math up for this. I have alittle picture drawn out and have everything labeled from the distance between the two trains to the bird's position, I just don't understand how to apply this to an equation much less account for the bird and train's change of position. Anyway I imagine you set it up as the point that the bird lifts off is the origin and have a variable to represent where the bird and train will meet with something like 0+x=x-51. But now looking at that it looks completely ****ed and I feel like I'm over looking some small thing that will make the lightbulb go off.
  2. jcsd
  3. Jan 14, 2010 #2
    Yeah I think you might be right. The half-point is 25.5km and it would take each train .75 hours (40 minutes) to collide. The bird's velocity is a given 60km/h so you would multiply 60(.75) to get 45km.
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