1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    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!

Doppler effect problem

  1. Dec 5, 2013 #1
    1. The problem statement, all variables and given/known data

    A parachutist leaps from a hovering helicopter, after 4.0s of freefall shouts back at 425Hz. What frequeny is heard at the helicopter?

    2. Relevant equations

    f'=f/(1+Vs/V)


    Vsource=?
    f'=?
    f=425Hz
    V=343m/s
    3. The attempt at a solution


    I'm stuck on finding the speed for the jumper. I'm sure it's simple but i just can't think of it for somereason.
     
    Last edited: Dec 6, 2013
  2. jcsd
  3. Dec 5, 2013 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member


    Read the problem carefully. It is free-fall, the parachute is not yet opened . What is the speed of a falling body after 4 s?

    ehild
     
  4. Dec 5, 2013 #3
    thinking
     
    Last edited: Dec 5, 2013
  5. Dec 5, 2013 #4

    vy=Vyi-gt right?

    initial speed is 0 so its just -9.8*4=-39.2
     
  6. Dec 6, 2013 #5

    ehild

    User Avatar
    Homework Helper
    Gold Member

    Yes, it is the velocity if you consider upward positive.
    The parachuter shouts back. How is his sound heard on the helicopter? (Hm. The helicopter is very noisy --think it is a super helicopter making only low noise so the parachuter's sound can be heard :wink:)


    ehild
     
  7. Dec 6, 2013 #6
    But it is strange that i get a higher frequency of what it should be. The answer is 381.4 and i keep getting 479. I'm getting my signs wrong somewhere...

    I used f'=f/(1+Vs/V) for a source moving away from reciever.
     
  8. Dec 6, 2013 #7

    ehild

    User Avatar
    Homework Helper
    Gold Member

    You need to calculate with the speed of moving away. The speed is positive, magnitude of velocity. Substitute Vs=39.2 m/s.

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

Have something to add?
Draft saved Draft deleted



Similar Discussions: Doppler effect problem
  1. Doppler Effect Problem (Replies: 0)

  2. Doppler Effect Problem (Replies: 1)

  3. Doppler Effect Problem (Replies: 8)

Loading...