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Homework Help: Basic newton's law.

  1. Nov 13, 2009 #1
    A 6.3 kg object is accelerated from rest to speed at 44 m/s in 35s.
    What average force was exerted on the object during the period of acceleration?
    Answer in units of N.

    i did f=mg
    so f=61.75
    then i divided by 35 and i got 1.764 N.
    is that correct?
    whats the velocity for then?

    Thank you!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 13, 2009 #2


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    Homework Helper

    Hi Ronaldo21, welcome to PF.
    F = mg is for freely falling body. You cannot use that formula here.
    Select the kinematic equation which contain initial velocity, final velocity, time and acceleration. And find the acceleration.
  4. Nov 13, 2009 #3


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    Gold Member

    Think about what equation you used. What does gravity, g, have to do with this? Then how would you divide a force by a time to return a force?

    To get to the answer, think about what is the definition of a force and an acceleration?
  5. Nov 13, 2009 #4
    OHH so i use a=(vf-vi)/change in time then??
  6. Nov 13, 2009 #5


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    Gold Member

    Yes, that gives you an acceleration. Then you know that F = ma, so you are one small step from finding the average force.
  7. Nov 13, 2009 #6
    oh okay i get it now.
    so i basicaly do 44/35 and get 1.25714
    then use f=ma so 6.3 times 1.25714 and get 7.92 right?
  8. Nov 13, 2009 #7


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    Gold Member

    Yup, you got it.
  9. Nov 13, 2009 #8
    Thank you! :d
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