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Homework Help: Avg. Velocity = Distance Traveled / Time Traveled

  1. Oct 15, 2007 #1
    Do you know if these two formulas are the same?

    Avg. Velocity = Distance Traveled / Time Traveled

    &

    Avg. Velocity = V1 + V2 / 2 (V1 = d1/t1 & V2 = d2/t2)

    I have a problem that says that a plain goes from a place to another(1) and from there it goes to another place (2).

    So:

    t1 = 3 h & d1 = 375 km
    t2 = 2 h & d2 = 250 km

    and using both of the formulas I get the same Average Velocity.
    So:

    Formula 1 = (375/3 + 250/2)/2 = 125 m/s
    ........................................................ ----> Formula 1 = Formula 2
    Formula 2 = (375 + 250)/(3+2) = 125 m/s



    So I'm guessing they are the same. But my science teacher says they're not.

    Do you agree with my teacher? How come?

    If you think its right, can you show me a mathematical way to prove it?

    Thanks.

    P.S. Please answer ASAP.
     
    Last edited: Oct 15, 2007
  2. jcsd
  3. Oct 15, 2007 #2

    Doc Al

    User Avatar

    Staff: Mentor

    You are only getting away with Formula 1 because the velocity is constant in your example. What if it wasn't constant?

    Say the plane moved a distance of 300 km in 2 hours, then an additional 300 km in 1 hour. Compare your formulas in this case.
     
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