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Homework Help: Difference in flight time for two planes with different velocity profiles

  1. Jan 25, 2017 #1
    1. The problem statement, all variables and given/known data
    ** sorry, answer in the book doesn't make sense **
    A british concord and a French concord flew in opposite directions around the world, a distance of 40K km. The BC covered half its distance at 2500 km/h, and the other half at 1000km/h. The FC spent half its flight time at 2500 km/h and the other half at 1000 km/h. Which concorde completed the trip first and by how many hours did it beat the oher?
    2. Relevant equations
    V= d/t.

    3. The attempt at a solution
    Time for BC

    20 000km /t = 2500
    t= 20 000/2500
    t= 8 hours
    20 000km/1000=t
    20 hrs = t
    Total time = 28 hours

    Time for FC
    40 000 = 2500 (t/2) + 1000 (t/2)
    40 000 = 3500 (t/2)
    (40 000/3500)2= t
    22.9 hours =t

    Looking at this, the french concorde got there first and beat the British concord by 5.1 hours. At the back, the difference I got is correct, it is 5.1 hours, but it says the British concord got there first. How? The BC trip was 28 hours, the FC trip was 22.9 unless I did something wrong ?

    *I'm sorry this is probably a dumb question, but I don't remember if my teacher said the answer at the back was incorrect or not, so this is me reconfirming my assumption that the book is wrong *
  2. jcsd
  3. Jan 25, 2017 #2
    It looks like the book is wrong.
  4. Jan 25, 2017 #3


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Your answer looks ok to me.
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