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Spring constant/kinetic energy

  1. Jul 17, 2009 #1
    1. The problem statement, all variables and given/known data

    If you stand on a bathroom scale, the spring inside the scale compresses 0.55mm, and it tells you your weight is 760 N.
    Now if you jump on the scale from a height of 1.3m, what does the scale read at its peak?

    2. Relevant equations
    F=kx
    K.E=1/2mv^2


    3. The attempt at a solution
    I tried alot of things but i cant get the answer
     
  2. jcsd
  3. Jul 17, 2009 #2
    Try more... :smile:

    Well one more equation you need to know

    Elastic potential energy = Eep = 0.5 kx2

    I'm sure you know how to get the spring constant, k
    And then find the total energy of the system E = mgh

    then substitute the E value you got to the equation
    Eep = 0.5 kx2 to find x

    (at the "peak", all of the kinetic energy + gravitational potential energy is converted to elastic potential energy)

    then since you know the x (compression) at the peak value
    substitute to F = kx to get the F value for the scale value it reads

    That's what i would do.
    I can very well be wrong
     
  4. Jul 17, 2009 #3
  5. Jul 18, 2009 #4
    Very well explained, V_B!
     
  6. Jul 18, 2009 #5
    Thx LOL ^^
     
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