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Homework Help: Simple question but stuck

  1. Oct 1, 2009 #1
    1. The problem statement, all variables and given/known data

    In order for a jumbo jet to take off, it must reach a final velocity of 360 km/h. Given that it moves at a constant acceleration and that the runway is 1.8 km long, find the minimum initial acceleration required to reach the final velocity. The jet starts at rest.

    2. Relevant equations
    V1^2 = V0^2 + 2a(x-x0)

    3. The attempt at a solution

    I tried putting the given values into this equation and nothing sensible happened. The acceleration is constant, so it should be the same at any point. Also, the jet starts at rest, so the velocity at time 0 is 0.

    I don't know what's going on, please help

  2. jcsd
  3. Oct 1, 2009 #2
    Everything is to be done in the x coordinate.

    360km/h = 100m/s = V(final), distance = 1800m

    Given that, and the formula "V1^2 = V0^2 + 2a(x-x0) ", you should be able to find acceleration.

    Which should be: 10000 = 0 + 3600a
  4. Oct 1, 2009 #3
    I put the same thing in terms of kilometers and meters, what's the difference?

  5. Oct 1, 2009 #4
    The units have to be consistent, acceleration = m/(s^2), so when plugging into the formula, length has to be in meters, and time has to be in seconds.
  6. Oct 1, 2009 #5
    ah right. thanks.. I was suspicious of that..

    this might sound stupid, but what's the easiest way to convert something into something else?

    Last edited: Oct 1, 2009
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