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Related rates, planes

  1. Mar 8, 2010 #1
    1. The problem statement, all variables and given/known data
    At ten am, a plane travelling east at 100km/hr is 500 km west of a jet traveling south at 200km/hr. At what rate is the distance between them changing at noon?

    2. Relevant equations

    3. The attempt at a solution
    2aa' + 2bb' = 2cc'
    2(300)(-100) + 2(400)(200) = (1000)c'
    -60000 + 160000 = 1000c'
    c' = 1000 km/h

    i need 186.1 km/h though.
  2. jcsd
  3. Mar 8, 2010 #2


    Staff: Mentor

    At noon, I find that the planes are moving apart at a rate of 100 km/hr at noon. I checked a couple of other times to see the rate at which the planes are moving apart. At 11am, the rate of change of distance was 0 km/hr. at 1pm, the rate of change of distance was about 158.1 km/hr. At 2pm, the rate of change is about 186.1 km/hr.

    Are you sure you've given us the right times?

    BTW, these are a couple of very slow planes. Many planes stall at speeds of 100km/hr, and a speed of 200km/hr for a jet is likewise very slow.
  4. Mar 8, 2010 #3
    yes, these are the times listed on my sheet. there may be a typo though.
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