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Stone resting on a spring

  1. Oct 13, 2004 #1
    I got parts a and b but am having trouble getting part c and d. can someone please help me? thanks in advance!

    Figure 8-40 shows an 8.00 kg stone resting on a spring. The spring is compressed 8.0 cm by the stone.

    Fig. 8-40

    (a) What is the spring constant?
    9.8 N/cm by mg/x(compression)

    (b) The stone is pushed down an additional 30.0 cm and released. What is the elastic potential energy of the compressed spring just before that release?
    70.8 J by convert A to N/m then convert compression to m and then use .5kx^2 to get the answer

    (c) What is the change in the gravitational potential energy of the stone-Earth system when the stone moves from the release point to its maximum height?
    J gravitational potential energy is mgy but i don't know y

    (d) What is that maximum height, measured from the release point?
    m y=(.5mv^2)/mg I know i have to use this eqn. but i don't know v.
     
  2. jcsd
  3. Oct 13, 2004 #2
    parts c) and d)

    (c) What is the change in the gravitational potential energy of the stone-Earth system when the stone moves from the release point to its maximum height?
    *** as you said, J gravitational potential energy is mgy but i don't know y, but from conservation of energy you know that dU = EPinitial (see answer B)...

    (d) What is that maximum height, measured from the release point?
    m y=(.5mv^2)/mg I know i have to use this eqn. but i don't know v.

    ** actually you don't have to use this equation.... we know dU = mg dy = EPinitial.... and now you can solve for height..
     
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