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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.
    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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