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Homework Help: Please Help With A Physics Problem

  1. Nov 10, 2007 #1
    here is the problem.

    A cannon shoots a 6 lb shell straight up. It reaches its maximum height, 1024 feet, and splits into two pieces, 2 lb and 4 lb. The two pieces are observed to strike the ground simultaneously. The 4 lb piece hits the ground 1600 feet away from the explosion(measured along the x AXIS)

    a. How long would it have taken the shell to return to the ground if it had not split?

    I found the TIME=8 seconds.

    b.Find the velocity of each of the two pieces just after the explosion.

    2lb piece - 400 ft/s
    4lb piece - 200ft/s

    AND PART "C" is where I get stuck!!! PLEASE HELP HERE.
    Here is part "C"

    c. Find the momentum of each piece just before they strike the ground.
    WHAT SHOULD I DO.
    Please Help

    The answer in the book is
    2lb piece - p(vector) = -25i(unit vector)x - 16i(unit vector)z
    4lb piece - p(vector) = 25i(unit vector)x - 32i(unit vector)z
     
  2. jcsd
  3. Nov 10, 2007 #2
    I know its something easy but i just can't get it :(
     
  4. Nov 10, 2007 #3
    Unless there's something I'm missing, you should be able to just use p=mv.

    Just make sure to use velocity at the instant of interest, not immediately after separation.
     
  5. Nov 11, 2007 #4
    I tried, but I don't know what to use for my initial momentum and my final momentum.

    It is just so weird looking... I mean.. the velocity is Vx +Vy but.. the numbers are too big to get such a numbers.

    i have no clue...
     
  6. Nov 11, 2007 #5
    If im not mistaken it dosent matter what mass something is. A 6lb. weight will hit the ground the same time as a 4lb and a 2lb as long as they are at the same height. And from what you said they spit at their max height.
     
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