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Acceleration formulas

  1. Aug 10, 2009 #1
    1. The problem statement, all variables and given/known data
    13. Which expression represents an equality between accelerations?

    A) Gme/r = v/r
    b) Gme/r2= v/r
    C) Gme/r2= v2/r
    D) √Gme/r= v/r2







    3. The attempt at a solution
    i have no idea how to figure this out.
     
  2. jcsd
  3. Aug 10, 2009 #2

    rock.freak667

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    If you can't automatically see it. Write out the units of each one and see if you get m/s2 on the left and right sides.

    Also, seeing the terms on the left side, do know a formula for acceleration? Do the same for the right side with the terms v and r.
     
  4. Aug 10, 2009 #3

    tms

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    It's a question of units. In which answer, if any, do the left- and right-hand sides both have the units of acceleration?
     
  5. Aug 10, 2009 #4
    so i know for sure answers b and c do, but what about the other sides. a=v/t is an equation, but thats not an option..
     
  6. Aug 10, 2009 #5

    tms

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    Since answers b and c are different in the right-hand side, they can't both be correct. It is a question of units, not of any particular equation that might represent an acceleration.
     
  7. Aug 10, 2009 #6
    but for v and r, it would be m2/s, rather than m/s2
     
  8. Aug 10, 2009 #7

    tms

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    v is m/sec, and r is m, so, for instance, v/r is
    [tex]\frac{\text{m/sec}}{\text{m}} = \frac{1}{\text{sec}}.[/tex]
    Is that acceleration? You have to do the same kind of "calculation" for each possible answer.
     
    Last edited: Aug 10, 2009
  9. Aug 10, 2009 #8
    o thank you!! that makes way more sense. :D
     
  10. Aug 10, 2009 #9
    i have one more question if u think you could answer it,
    -When the distance separating two masses, M and m, is 1.2 x 1010 m, the gravitational force of attraction is 5.0 N. If the mass of M becomes 3M and the separation distance becomes
    2.4 x 1010 m, what will be the force?

    A. 0.27 N
    B. 2.2 N
    C. 3.8 N
    D. 7.5 N

    what equation am i suppossed to use for that??
     
  11. Aug 10, 2009 #10

    rock.freak667

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    gravitational force of attraction

    Maybe a formula that contains M,m and an r ? Perhaps a constant like G in it as well.
     
  12. Aug 10, 2009 #11

    tms

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    You're supposed to use the equation for for the gravitational force between two bodies.

    You should also start a new thread for a new question, so other people can find it easily.
     
  13. Aug 10, 2009 #12
    but taht formula doesnt have force in it.
     
  14. Aug 10, 2009 #13

    tms

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    Sure it does; it defines the force.
     
  15. Aug 10, 2009 #14
    o sorry. i will know for next time. and ok. so Fg=GmM/r^2. but in the equation it tells us the distance between the two. not what each equals. how do i solve that?
     
  16. Aug 10, 2009 #15

    tms

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    You can write two equations: one for the initial conditions, and one for the second set of conditions. G is known; you are given the force in the first situation, and the distances; you are given the second set of masses in terms of the first; but you don't know the masses m and M. You need to somehow get rid of m and M from the equations. If you actually write down the equations, the technique should jump out at you.
     
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