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Homework Help: Spring work Question

  1. Oct 10, 2004 #1
    Okay I have figured out parts a-c but I cannot figure out part d. Here's the question and my answers I have gotten so far:

    A 260 g block is dropped onto a relaxed vertical spring that has a spring constant of k = 2.5 N/cm (Figure 7-42). The block becomes attached to the spring and compresses the spring 13 cm before momentarily stopping.

    Fig. 7-42

    (a) While the spring is being compressed, what work is done on the block by the gravitational force on it?
    (b) What work is done on the block by the spring force while the spring is being compressed?
    (c) What is the speed of the block just before it hits the spring? (Assume that friction is negligible.)
    (d) If the speed at impact is doubled, what is the maximum compression of the spring?

    I tried using the eqn. .5m(2v)^2=mgx-.5kx^2 and it did not work...what did i do wrong??? Thanks in advance!!
  2. jcsd
  3. Oct 10, 2004 #2
    Does ANYBODY have ANY ideas??
  4. Oct 10, 2004 #3
    you have to double the answer you got from C and that will become your new velocity. then you have to do mgd-1/2kd^2=-1/2mv^2 and you solve for d. Hope this helps.only thing i noticed you did wrong was you didn't put the negative in front of 1/2mv^2. :smile:
  5. Oct 10, 2004 #4
    Thanks a lot! I forgot a negative sign.
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