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Block on Incline with oscillation

  1. Dec 11, 2009 #1
    1. The problem statement, all variables and given/known data

    Block on Incline In Fig. 16-35, a block weighing 17.0 N is able to slide without friction on a 32.0° incline. It is connected to the top of the incline by a massless spring of unstretched length 0.475 m and spring constant 110 N/m.

    Figure 16-35

    (a) How far down the incline would you have to place the block so it would not oscillate when you let go?
    1 m
    (b) If the block is pulled slightly down the incline from where you placed in part (a) and released, what is the period of the resulting oscillations?

    2. Relevant equations

    I got part b, just need part a.

    I was told that Force(spring) = Force(gravity)

    (Fs) = kx
    (Fgrav)= mgcos(theta) since on an incline

    3. The attempt at a solution

    The force of spring = kx and
    The force of grav = mg cos(theta)

    By doing this my answer should be x = [ mg cos (theta) ] / k
    which comes out to be about 1.284

    This showed up as incorrect. Some guidance about what I'm doing wrong is greatly appreciated.

    I had posted in another thread a few hours ago and no one responded... but it was one that already had many posts so I guess people just ignored it.
  2. jcsd
  3. Dec 11, 2009 #2


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    Homework Helper

    Force of gravity = mg*sin(theta)
  4. Dec 11, 2009 #3
    I already tried that and it was wrong. I got .8026 for my answer and I even tried doing sin and cos of 40 degrees. None of them worked. I looked on cramster and found the same problem since no one had been answering my other post and I found that they got the right answer using the formula I stated above. Their m was 10 N, k was 150 and theta was I believe 37 or 38, I think 38 and the answer was .515 and correct. Having really bad luck I guess. Anything else you might suggest I try? I really can't think of another formula that would work.
  5. Dec 11, 2009 #4
    I figured it out. They give the weight as 17.0 N which is mg so I was doing g squared at first. When I got my answer with that, I added it to the initial distance and got it right. Got it on the 10th try out of 10 as well :) Thanks for trying though hehe. Was just a pure coincidence that the cos worked for the other problem.
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