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Homework Help: SHO energy problem

  1. Apr 4, 2007 #1
    A 0.0125 kg bullet strikes a 0.300 kg block attached to a fixed horizontal spring whose spring constant is 2.25 * 10^3 N/m and sets it into vibration with an amplitude of 12.4 cm. What was the speed of the bullet if the two objects move together after impact?

    E = .5 k A2 = .5 m v2
    Do I use m = mass of bullet + mass of block, or just the mass of the bullet?
    Using the former, I get v = 10.5 m/s. Is this right? It just seems kind of slow for a bullet...
  2. jcsd
  3. Apr 5, 2007 #2
    This is an energy conservation problem

    Initially the only energy is the kinetic energy of the bullet.

    Finally, the only energy is the spring energy (potential+kinetic).

    Those two energies are the same.
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