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Block ramp friction and spring

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data
    A 5 kg block is placed near the top of a frictionless ramp, which makes an angle of 30o degrees to the horizontal. A distance d = 1.3 m away from the block is an unstretched spring with k = 3000 N/m. The block slides down the ramp and compresses the spring. Find the magnitude of the maximum compression of the spring.



    2. Relevant equations
    quadratic equation ax+bx-c
    h=d+xsintheta
    PE=mgh=mg(d+x)sintheta
    PE=1/2kx

    mg(d+x)sintheta=1/2kx
    0=1/2kx+-mg sintheta +-mgd sintheta
    ax+bx-c


    3. The attempt at a solution

    What i did was plug in the numbers into the quadratic equation and i thought that is all that i had to do.. and the answer is still not correct. if someone could please help me out that would be appreciative =)
     
  2. jcsd
  3. Oct 20, 2009 #2

    ehild

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    Homework Helper
    Gold Member

    Your formula for PE is wrong. PE=1/2kx2.
    You have to solve your quadratic equation of form ax2+bx+c=0.

    ehild
     
  4. Oct 21, 2009 #3
    I just tried figuring it out once again..

    a=1500
    b=48.463
    c= 63.002


    so then i used the quad equation to solve for X


    x= -b +- squareroot b2-4ac / 2a

    and x comes out to either be

    x= .0506461
    x= -.0829547

    then i put it back into the equation
    PE=.5(k)(x)

    and i tried both.. one i got around 3 and the other i got around 10

    what else am i doing wrong that i cant figure this out?
     
  5. Oct 21, 2009 #4

    ehild

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    Homework Helper
    Gold Member

    What does it mean "maximum compression of the spring"? And what is "x" for?

    ehild
     
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