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-   -   Please help in numerical.. (https://www.askmehelpdesk.com/showthread.php?t=702395)

  • Sep 16, 2012, 09:30 AM
    lionel messi
    Please help in numerical..
    An object weighing 98N is dropped from a height of 10m. It is found to be moving with a velocity 12m/s just before it hits the ground. How large was the frictional force acting upon it?
    Will it be done by using k.E=P.E+W in which -26N ANSWER is coming. If yes,than can it be solved via equations of motion (than f=ma)..
  • Sep 16, 2012, 09:45 AM
    Unknown008
    Both methods can be used.
  • Sep 16, 2012, 09:52 AM
    lionel messi
    But answers are different?? I think 26N is the right answer which I am getting from work energy equation. But can't from equ of motion?
  • Sep 16, 2012, 10:03 AM
    Unknown008
    Show your work of how you reached 26 N please.
  • Sep 16, 2012, 10:08 AM
    lionel messi
    0.5mv^2-mgh=F.S
    0.5*10*12^2 - (10*9.8*10)=f.s
    -260N=F(10)
    F=-26N..
  • Sep 16, 2012, 10:09 AM
    Unknown008
    Okay, how did you do for the equation of motion?
  • Sep 16, 2012, 10:13 AM
    lionel messi
    I am getting different answers.but not 26N.. Can u solve it please..
  • Sep 16, 2012, 10:14 AM
    Unknown008
    No no, I want you to post what you tried. There's nothing wrong with making a mistake. You learn from mistakes after all.
  • Sep 16, 2012, 10:20 AM
    lionel messi
    Here vi=0 or vf=0..
  • Sep 16, 2012, 10:22 AM
    Unknown008
    I won't answer anything more until you post what you tried, from the start to the final answer you got that you're saying is wrong.
  • Sep 16, 2012, 10:27 AM
    lionel messi
    Ive delivered my try before as well..
    If vi=0 than,
    f=ma
    =10*(vf-vi)/t
    =10*(12/1.428)
    =84N.. WHERE t from 2nd equ of motion
  • Sep 16, 2012, 10:31 AM
    Unknown008
    Okay, I'm not sure why you tried to use something you have to calculate here.

    I would use

    v = 12
    u = 0
    a = ?
    s = 10





    This is the net acceleration of the object.







    This is the acceleration due to friction.

    F = ma

    F = 10*2.6 = 26 N
  • Sep 16, 2012, 10:35 AM
    lionel messi
    Thanks mate..

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