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Homework Help: What was the jets speed from bangkok to tokyo

  1. Aug 18, 2010 #1
    Hi i am stuck on this question i feel like i am missing information to solve it.


    A jet flew from Tokyo to Bangkok, a distance of 4800km. on the return trip, the speed was decreased by 200km/h. if the difference in times of the flights was 2 hours, what was the jets speed from bangkok to tokyo.
     
  2. jcsd
  3. Aug 18, 2010 #2

    Mark44

    Staff: Mentor

    What have you tried? What are the relevant formulas?
     
  4. Aug 18, 2010 #3
    i have tried to work up a formula using speed=distance/time and in previous questions i would have to put it into ax^2+bx+c form and then factor to find the x intercepts but this time it isnt working for me.
     
  5. Aug 19, 2010 #4

    Mentallic

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    Homework Helper

    What are the equations you've tried to set up using the distance = speed * time formula? You should have two equations in terms of velocity and time, which you can then eliminate time and solve for velocity.
     
  6. Aug 19, 2010 #5
    i had a previous question that said the total round trip was 13 hours so what i did there was

    4800/x+4800/x-200=13 and then eventually solved the equation

    but now i dont know what to do because the equation looks like this for me

    4800/x +4800/x-200=2 and that dosn't seem to work out for me
     
  7. Aug 19, 2010 #6

    Mentallic

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    No, this question is slightly different and you can make things much easier on yourself if you create two equations and solve them simultaneously - even for the previous questions you've been answering.

    The first equation involves the travel to and the second from.

    Use [tex]\frac{d}{v}=t[/tex] where d=distance, v=velocity, t=time

    This formula will apply to both equations, but think carefully about what the velocity and time are going to be for each of them. Say if you let v be the velocity of the plane when headed to its destination, then what will the velocity be in terms of v when headed back?
     
  8. Aug 19, 2010 #7
    thanks for your help mentallic but i am still very confused. i don't know what you mean by "the first equation involved the travel to and the second form."
     
  9. Aug 19, 2010 #8

    Mentallic

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    You are going to have to create two equations. Each will involve the variables v and t which is for velocity and time respectively. You first equation is going to be describing the journey to its destination, again, use d=vt and plug in what you know and keep what you don't know a variable. The second equation will be the journey back and you still use d=vt but you change some things such as how it says the speed is decreased by 200 km/h so you use (v-200) to substitute into the velocity part of the formula. Can you take it from here?

    EDIT: I went off elsewhere and didn't simply answer your question. I spoke loosely with my words, I meant the first equation will describe your journey to its destination and your second equation will describe your journey back.
     
  10. Aug 19, 2010 #9
    hah yes thank you very much for your help i figured out what i was doing wrong
     
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