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Homework Help: Bullet colliding into spring

  1. Jan 25, 2010 #1
    1. The problem statement, all variables and given/known data

    A 4kg block resting on frictionless surface is attached to spring of k=100n/m. A 2g bullet is fired at 100m/s at the block. What is the period and amplitude of oscillations?

    2. Relevant equations

    1/2mv2 = kinetic energy
    1/2kx2 = elastic energy
    2 x pi x square root (mass/k) = period

    3. The attempt at a solution

    No answer choices given, just seeing if my thought process is valid.

    First, period. 2 x pi x square root (4/100) = 2 x pi x 2/10 = 4pi/10 = approx. 1.2

    Next, amplitude. 1/2 (.002g) (100m/s2) = 1/2 100n/m x2
    therefore, x equals out to .45, or 45 cm?

    Does this make sense, I think I have the period right, but one of my friends got 1 cm for the amplitude and another one of my friends got 0.83 seconds for the period. Any ideas?

  2. jcsd
  3. Jan 26, 2010 #2
    There's been a mistake.
    You took an inelastic collision for a completely elastic one.Instead conserve momentum to find velocity of bullet-block system and then proceed for momentum.
  4. Jan 26, 2010 #3
    That makes great sense. Thanks
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