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Homework Help: Energy of SMH

  1. Dec 15, 2005 #1
    I have 3 questions. I will give you what I think is the answer and you can either give me the answer or lead me in the right direction. I appreciate both equally. With direction I can find the answer, and with the answer I can find the direction, so I am cool either way.

    When the compression of a spring is reduced to half it's original value, the potential energy stored in the spring is:

    1/8 original value.
    1/4 original value.
    The same as above.

    I think it is the same because, if I remmber right, E = 1/2mv^2 and isn't affected by compression.

    The total energy of a spring undergoing SHM could be expressed as:
    E = 1/2mv^2, correct?

    This is the one I am clueless on:

    A 2.5 kg object is attached to a spring of force constant k = 4.5 kN/m. The spring is streched 10 cm from the equilibrium and released. What is the kinetic energy of the mass-spring system when the mass is 5 cm from tits equilibrium position?

    14 J
    11 J
    17 J

    No clue. I think I am using the wrong formulas or factoring in A and Xmax incorrectly or something. Any help would be great on this one.

  2. jcsd
  3. Dec 15, 2005 #2


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    Homework Helper

    Potential energy of a spring: (1/2)kx2.
    E = K + U, where K is kinetic energy and U potential energy, so E = (1/2)mv2 is incorrect.

    Can you now solve the problem?
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