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Homework Help: Spring force

  1. Jul 30, 2006 #1
    A spring with length l = 8 cm hangs in
    vertical direction somewhere close the earth's surface. When a mass of m = 10 kg is attached
    to the spring its rest-position is at y0 = 11 cm. (a) Determine the spring constant k.

    i try to use F=-kx = mg where x=11cm - 8cm
    therefore,i would like to know whether my steps are correct or i used the wrong formula

    somebody pls help
     
  2. jcsd
  3. Jul 30, 2006 #2
    part b) The
    mass is pulled out of its rest-position by a distance Δy = 5 cm. What is the acceleration acting
    on the mass in the moment of its release?

    i got the answer of a=16.35m/s^2

    am i right??
     
  4. Jul 30, 2006 #3
    You're in the right direction :) Remember that at the spring its rest position [tex]F_{gr.} = F_{spring} = C \cdot u[/tex] where C = spring constant.

    So you need to solve: [tex] m \cdot g = C \cdot u[/tex] with u = distance of strecthing of the spring (3 cm)
     
  5. Jul 30, 2006 #4
    foir b i would say that you use the second law of Newton: [tex] F_{res} = m \cdot a[/tex]
     
  6. Jul 30, 2006 #5

    Doc Al

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    Staff: Mentor

    You are correct. (Except for that minus sign. Set the magnitude of the spring force equal to the magnitude of the weight.)
     
  7. Jul 30, 2006 #6

    Doc Al

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    Staff: Mentor

    Looks OK to me. (But next time don't just give your answer; show how you got your answer. :wink: )
     
  8. Jul 30, 2006 #7
    agrees with Doc Al :)
     
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