Sonic Booms

Standard memberRamned
Science 04 Mar '08 23:34
  1. Standard memberRamned
    The Rams
    Joined
    04 Sep '06
    Moves
    13491
    04 Mar '08 23:34
    A bullet is fired from a powerful gun 5 meters above the head of an observer who is 150 m away. The observer hears 2 loud "cracks."

    A) Why does the observer hear 2 cracks?
    B) Which of the two cracks does the observer hear first? Why?
  2. Cape Town
    Joined
    14 Apr '05
    Moves
    52945
    05 Mar '08 08:29
    Originally posted by Ramned
    A bullet is fired from a powerful gun 5 meters above the head of an observer who is 150 m away. The observer hears 2 loud "cracks."

    A) Why does the observer hear 2 cracks?
    B) Which of the two cracks does the observer hear first? Why?
    The bullet traveled faster than sound.
    As the bullet leaves the gun it emits a 'crack' lets call it A.
    As the bullet is traveling, it slows down to less than the speed of sound, and thus emits a 'sonic boom', call it B.
    The observer will hear B first.
  3. Joined
    07 Sep '05
    Moves
    35068
    05 Mar '08 10:29
    Originally posted by twhitehead
    The observer will hear B first.
    On the second point - it is probably possible, if the initial velocity of the bullet was high enough, that the sonic boom caused by the deceleration through the speed of sound could happen some time after it had passed the observer. In which case you might hear it later.
  4. Cape Town
    Joined
    14 Apr '05
    Moves
    52945
    05 Mar '08 10:50
    Originally posted by mtthw
    On the second point - it is probably possible, if the initial velocity of the bullet was high enough, that the sonic boom caused by the deceleration through the speed of sound could happen some time after it had passed the observer. In which case you might hear it later.
    Good point, I didn't think of that. Maybe we should fire the gun directly at the observer so that we can be certain. 🙂
  5. Joined
    02 Aug '06
    Moves
    3992
    05 Mar '08 15:45
    Originally posted by twhitehead
    The bullet traveled faster than sound.
    As the bullet leaves the gun it emits a 'crack' lets call it A.
    As the bullet is traveling, it slows down to less than the speed of sound, and thus emits a 'sonic boom', call it B.
    The observer will hear B first.
    I think that the observer can hear A first, B first, or both of them at the same time - depending on the observer's position relatively to the bullet's trajectory.
Back to Top