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Homework Help: Momentum problems

  1. Nov 7, 2005 #1
    Problems Shortened
    1) Rocket fired up, when it reaches 300 m/s and 1000m, it explodes into three pieces. One contnues up at 450 m/s and the other continues east at 240 m/s. Third velocity?
    used conservation of momentum with components
    found that the velocity of the third piece had an x-component of -240 m/s and y-component of 450 m/s. solved and got 510 m/s. did i approach this problem correctly?
    2) Two people standing on a crate on a frictionless frozen pond. One person weighs 75 kg, the other 45 kg and the crate 15 kg. They jump horizontaly from the top of the crate. Just after each jumps, the person moves away from the crate at 4 m/s relative to the crate.
    a)What is the speed of the box if both jump off?
    MVi = MVf
    135(4) = 15(V)
    V = 36 m/s
    i have a feeling that i wdid that incorrectly
    b)What is the speed the 75 kg jumps off and then the
    45 kg person jumps off a few seconds later?
    135(4) = 60V V= 9 velocity after one person
    60(9) = 15V
    V= 36
    i also have a feeling that i did this one
    incorrect since a and b are both the same
    3)Cannon fires 100kg shell 60 degrees at 600 m/s. at highest point it explodes into two fragments (m1 = 2/5M and m2 = 3/5M), with an additional 10kJ of energy in the original horizontal direction. Whats the distance between the two pieces?
    honestly for this one i am lost. i dont expect it to be solved, but could someone possible guide me through it? or get me started?
  2. jcsd
  3. Nov 7, 2005 #2
    First: x-component was correct but y is wrong.
  4. Nov 7, 2005 #3
    can anyone give me a clue in finding the y-component?
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