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Momentum + Explosion

  1. Sep 5, 2016 #1
    1. The problem statement, all variables and given/known data
    A grenade is falling from the height 19.6m .Finding velocity of both masses(fragments), if m1 is equal to 2 times of m2

    ddg.png
    2. Relevant equations
    Conservation of Momentum
    v2 = u2 + 2as

    3. The attempt at a solution
    I think this is a pure mathematic problem :/ I can cut the mass out of my equation but I stuck with the velocities of the both masses
     
  2. jcsd
  3. Sep 5, 2016 #2
    So, what you need to do is to resolve the m1 and m2 into both x & y component. After that, solve the system by applying the momentum conservation principle at both X and Y component.
     
    Last edited by a moderator: Sep 6, 2016
  4. Sep 6, 2016 #3
    I got
    m2 about 47
    m1 anout 35
    lol
     
    Last edited by a moderator: Sep 6, 2016
  5. Sep 6, 2016 #4

    Merlin3189

    User Avatar
    Gold Member

    Looking at the horizontal components,
    m1 x v1 cos37 should equal 2m1 x v2 cos 53
    m1 x 30.2 cos37 = 24.12 m1 and 2m1 x 50.3 cos 53 =60.54 m1 which does not match.

    I take it, these are the velocities of those masses, so v2 about 47 v1 anout 35, so horizontal components of momentum,
    m1 x 35 cos37 = 28 m1 and 2m1 x 47 cos 53 = 57 m1

    Perhaps we can see your full working, then have more chance of spotting errors. My own arithmetic juggling is not that good and I had to rework it a couple of times when my checks did not come right. (I managed to swap v1 and v2 on my way through the calculation!)

    BTW for the final answer I assume the grenade explodes after it has fallen 19.6m. The question is a bit vague. Maybe it is dropped from 19.6m but explodes halfway down! On the other hand, if it is falling from 19.6m and explodes after it has fallen 19.6m, then it is on the ground and I think that would make a difference.

    Edit: removed a comment about the sign of the velocity, which was not helpful.
     
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