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Mass And Spring

  1. Oct 21, 2004 #1
    A 7.00 kg mass hanging from a spring scale is slowly lowered onto a vertical spring, as shown in the figure.

    I got the first part, What does the spring scale read just before the mass touches the lower spring? wich was, 68.6 N

    Dont understand how to approch, The scale reads 20.0 N when the lower spring has been compressed by 1.50cm . What is the value of the spring constant for the lower spring?....i know im trying to find k

    and also, At what compression length will the scale read zero?

    wouldnt this be when the mass is all the way on the spring?
     

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  3. Oct 21, 2004 #2
    anyone got any help?
     
  4. Oct 21, 2004 #3

    Pyrrhus

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    Homework Helper

    Do the forces analysis and Remember Hooke's Law [itex] F = kx [/itex] or in Vectorial form [itex] \vec{F} = k \vec{x} [/itex]
     
  5. Oct 21, 2004 #4
    still wondering, i know F=kx, F, being 68.6 and x = 1.5 cm, right? but that k isnt the right answer. i must be doing it wrong, but what?
     
  6. Oct 21, 2004 #5

    Pyrrhus

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    You know springs has a restorative force that will restore the spring back to its equilibrium position.
     
  7. Oct 21, 2004 #6

    Doc Al

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    Staff: Mentor

    It doesn't seem that you've made use of the given information: that the scale reads 20 N. If the scale reading is 20 N, what must be the force the spring is exerting on the mass?
     
  8. Oct 22, 2004 #7
    ALRIGHT, heres what i did, mupltipled, 68.6*48.6=3333.4 put that in for my homework online and it says i have a rounding error, i tried 5 diffrent things and it says the same thing, now i have 2 trys or i get a 0, anyone know whats wrong?
     
    Last edited: Oct 22, 2004
  9. Oct 22, 2004 #8

    Doc Al

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    Staff: Mentor

    I have no idea what you are up to with that calculation! Looks like you randomly multiplied two numbers. :mad:

    But... if the scale reads 20 N, that means the spring must be providing 68.6-20 = 48.6 N of force. The amount of compression associated with that spring force is given as 1.5 cm. Use F = kx to find k. (Careful of units!)
     
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