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Supersonic plane at mach 3

  1. Apr 15, 2012 #1
    1. The problem statement, all variables and given/known data

    A supersonic plane flies at Mach 3 at an altitude of 20,000 m. A person on the ground sees the plane directly overhead. How much time passes the before she hears the sonic boom?

    2. Relevant equations

    f=fo(v+-vo/v-+vs)

    3. The attempt at a solution

    I don't really know how to start up with this one, I was hoping for some help here.
     
  2. jcsd
  3. Apr 15, 2012 #2

    PeterO

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    The sonic boom is just a noise produced by the plane, which has to travel 20,000m to reach you.
    The answer would be the same if it was a helicopter hovering at 20000m then firing a really loud gun - or with a really big sound system playing AC-DC.
     
  4. Apr 15, 2012 #3
    So what equation do you suggest I can use to start up the problem?
     
  5. Apr 15, 2012 #4

    PeterO

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    You want to calculate the time taken for sound to travel 20000m. What equation do you think you need - it connects speed, time and distance?

    You will need to know the speed of sound - and will probably have to make the assumption that it remains constant all the way from up there to down where you are!
     
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