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Homework Help: Spring constant

  1. Feb 20, 2006 #1
    A spring scale is stretched 10 cm when a force of 15 N is applied to it. How far apart should adjacent 1.0 N marks be on the scale?

    Why would 1.5 cm not be correct?

    Force= Spring Constant* Change in spring from rest
    15n=k*10 cm
    k=1.5
     
  2. jcsd
  3. Feb 20, 2006 #2
    Wouldn't it be 0.66 cm? If there are 15 marks within 10 centimeters, there should be a mark every 2/3 of a centimeter. I may be reading this question wrong, though.
     
  4. Feb 20, 2006 #3
    For starters, watch the units! You are dividing N by cm! :grumpy: NOT a good habit to get into. The good news is, since you are using this k to calculate a distance in cm you can get away with it.

    Otherwise:
    F = kx
    15 N = k(10 cm)
    k = 15 N/10 cm = 1.5 N/cm.

    Now, set F = 1 N. (Since F is linear in x, this will be the separation between 1 N marks.)

    F = kx
    1 N = (15 N/cm)x
    x =1 N/(15 N/cm) = 0.66667 cm.

    My tip to all my students, anyways, is to ALWAYS write out your work, even if it seems easy enough to do in your head. (Perhaps especially when!)

    -Dan
     
  5. Feb 20, 2006 #4
    your right. I had everything flipped in my head
     
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