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Homework Help: Rotational Motion and Law of Gravity

  1. Nov 7, 2011 #1
    a) Two objects attract each other with a gravitational force of magnitude 9.30 x10-9 N when separated by 19.4 cm. If the total mass of the objects is 5.06 kg, what is the mass of each?

    Heavier mass_______kg
    Lighter mass______ kg

    my attempt:
    F=Gm1m2/r^2
    so I rearranged to get m1 and m2 by itself and got (r^2)(F)/G=m1m2
    5.247598=m1m2
    but how do I get the mass for m1 and m2 separately is m1 + m2 = 5.06 kg?


    b) A dental bracket exerts a horizontal force of 86.2 N on a tooth at point B in the figure. What is the torque on the root of the tooth about point A? (PLEASE SEE THE ATTACHMENT FOR THE PICTURE)

    I know I need to break the forces up into components but I am lost on this question. Please help me! Thank you
     

    Attached Files:

  2. jcsd
  3. Nov 7, 2011 #2

    gneill

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    Staff: Mentor

    Yes, the total mass is given as 5.06 kg, so m1 + m2 = 5.06 kg. Replace one of the masses, say m2, with m2 = (5.06 kg - m1).
     
  4. Nov 7, 2011 #3
    I used this and found my answer to be .433 and 4.627 but its wrong. Do i have my formula correct?
     
  5. Nov 7, 2011 #4

    gneill

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    Staff: Mentor

    Your formula (Newton's law of gravitation) looks okay. Perhaps something went wrong in your math manipulations. If you post your calculations they can be checked.
     
  6. Nov 7, 2011 #5
    actually I just solved it! It was just a silly error! But thank you for your help

    Do you have nay idea how to do part b ?
     
  7. Nov 7, 2011 #6

    gneill

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    Staff: Mentor

    What are your thoughts? What do you think you need to know in order to proceed?
     
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