1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    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


    User Avatar
    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


    User Avatar
    Homework Helper

    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


    User Avatar
    Homework Helper

    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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook