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A bullet with mass of 0,005g hits a wooden block with a mass of 1,2kg velocity

  1. Mar 8, 2009 #1
    1. The problem statement, all variables and given/known data
    A bullet with mass of 0,005g hits a wooden block with a mass of 1,2kg. The bullet and the block move 0,3meters after the collision, friction coefficient is 0,2 between the ground and the block. Find out velocity of the bullet.

    Trying to study for exams, but got stuck in this question


    3. The attempt at a solution


    V1 = ?
    V2 = ?
    m1 = 0,005kg
    m2= 1,2kg
    l = 0,3m
    u= 0,2

    we know that kinetic energy of the bullet is 1/2mv^2, after the bullet hits the block, the kinetic energy is converted into friction work, that is needed to move the block

    so 1/2mv^2 = Fu * 0,3m
    v^2 = ( 2 ( 0,005kg+1,2kg) * 9,8m/s^2 * 0,2 * 0,23m) / 0,005kg
    and v= squareroot ( ....)

    what am I doing wrong?
     
  2. jcsd
  3. Mar 8, 2009 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Hi pirates! :smile:
    No, this is an inelastic collision … energy is not conserved at the start …

    for the start, you have to use conservation of momentum :smile:
     
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