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Two Physics Problems plsss help ?

  1. Dec 22, 2006 #1
    Two Physics Problems .. plsss help ??!!

    Q1 :

    The figure shows a mass M inside a tube bent in a circle of radius R=1.20 m. M can slide with negligible friction inside the tube. The tube rotates about a vertical axis passing through the center. The mass is in equilibrium at q =56.5 degrees. Calculate the number of revolution the hoop makes in 12.0 s.

    THE FIGURE : http://www3.0zz0.com/2006/12/22/10/35335598.gif

    Q2:

    A 8.40 kg mass suspended from a spring with spring constant, k = 800.0 N/m, extends it to a total length of 0.270 m. Find the total length of the spring when a 13.40 kg mass is suspended from it.
     
  2. jcsd
  3. Dec 22, 2006 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    You will have to show what you have done to attempt a solution.

    AM
     
  4. Dec 22, 2006 #3
    the second question :i don't know how to begin !!!
    ............
    the first question

    F=kx, where F is the force applied, k is the spring constant and x is the distance stretched.

    k = 800 N/m
    x=0.270
    F=kx=800*0.270=216N/m

    I don't know how to find the total length of the spring ..

    [ i never learn physics before .. i have many problems !! I'm trying to be better ..]
     
  5. Dec 22, 2006 #4

    Doc Al

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    Staff: Mentor

    Careful: 0.270 m is the total length of the spring, not the amount of stretch. Use Hooke's law to figure out how much the spring stretched when the weight was added--this will allow you to calculate the unstretched length.

    Hint for question #1: What kind of motion does the mass undergo? What kind of acceleration?
     
  6. Dec 22, 2006 #5
    ok ..

    in question 2 :

    maybe i have to do that :

    F=mg=13.40*9.81=131.454 N

    x=F/k=131.454/800=0.1643m


    is it right ??
     
  7. Dec 22, 2006 #6

    Doc Al

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    Staff: Mentor

    That's certainly an essential step in solving the problem. What is the meaning of what you have calculated, and how does it relate to the final solution?
     
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