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Object is accelerated from rest , find KE

  1. Jan 5, 2015 #1
    1. The problem statement, all variables and given/known data

    An object is accelerated from rest by a force of 32 N over a distance of 18 m. Calculate the
    kinetic energy of the object after 18 m

    2. Relevant equations

    KE = 0.5 • m • v^2


    3. The attempt at a solution

    I cant work out where ill be able to get the mass or the velocity for this one?
     
  2. jcsd
  3. Jan 5, 2015 #2

    Doc Al

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    Staff: Mentor

    Hint: Maybe you won't need those quantities. Any other principles you know that have to do with energy?
     
  4. Jan 5, 2015 #3
    You can work them out if you wish , if we can put 'a' in term of 'm' [From the given force] , we can find the final velocity using the equations of motion with constant acceleration [the acceleration is constant because the force is constant] .

    But this method is quite long .However, as Mr @Doc Al said, there is a shorter method that has to do with work and energy , could you figure it out?

    :)
     
  5. Jan 5, 2015 #4
    ummm

    well the force by the distance will give me the work done

    32 x 18 = 576J

    Im almost sure there is a relationship between work and KE but i cant work out what ?:)
     
  6. Jan 5, 2015 #5
    Well, have you studied Work-Kinetic energy theorem ?
     
  7. Jan 5, 2015 #6
    Yes but im not sure i totally understand what to do when with the formula we have

    2ufq5jp.png
     
  8. Jan 5, 2015 #7

    Doc Al

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    Staff: Mentor

    That's the formula you need! What does it say? (In words.)
     
  9. Jan 5, 2015 #8
    If im totally honest Im not sure what KEf and KEo stand for .
     
  10. Jan 5, 2015 #9
    Work-Kinetic energy says :
    "For a particle , a change in the kinetic energy equals the net work done on the particle "

    In the formula you give :

    KEf stands for final kinetic energy of the object.
    KE0 stands for initial kinetic energy of the object.
     
  11. Jan 5, 2015 #10
    I Hope you get the point now ,,.
     
  12. Jan 5, 2015 #11
    Ah so the work done is the same as the KE !

    I know the work done is 576J so thats the same as the KE!

    thanks for your help :)
     
  13. Jan 5, 2015 #12
    The work done is equal to the value of KEf - KE0 But KE0 is zero since the object has started from the rest [the velocity is zero] so the final kinetic energy is equal to the work done by the object..


    :)
     
  14. Jan 5, 2015 #13
    Oh perfect i actually over looked that! thaks again for your help!
     
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