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Applying Force On An Angle

  1. Feb 4, 2007 #1

    danago

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    Gold Member

    1. The problem statement, all variables and given/known data
    A lawnmower weighing 20kg has a handle attached at 35 degrees to the horizontal. If a man wishes to push the lawnmower, so that after 2.5s, its velcoity is 2 m/s, what force should he apply along the handle.

    2. Relevant equations
    [tex]
    \sum {\overrightarrow F } = m\overrightarrow a
    [/tex]

    3. The attempt at a solution
    ok, since after 2.5 seconds, it requires a velocity of 2 m/s, i found the acceleration of the mower to be 0.8 m/s/s. Since it has a mass of 20kg, the net force applied must then be:

    [tex]
    \sum {\overrightarrow F } = 20 \times 0.8 = 16N
    [/tex]

    So the horizontal component of the force he applies must be 16N in the direction of acceleration.

    The horizontal component of the force (F) he applies down the handle will be [tex]F cos 35[/tex]. So solving for F:

    [tex]Fcos35=16[/tex]

    Gives F=19.5N.

    According to the answer book, the answer is 120N. Where have i gone wrong?

    Thanks,
    Dan.
     
    Last edited: Feb 4, 2007
  2. jcsd
  3. Feb 4, 2007 #2

    Hootenanny

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    If the question is quoted correctly, then I would agree with your answer. Does the text not mention any other factors, such as friction?
     
  4. Feb 4, 2007 #3

    danago

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    Nope, no friction at all. What ive said is pretty much quoted word for word from the book.

    Thanks for the reply.
     
  5. Feb 4, 2007 #4
    yeah the book is def. wrong
     
  6. Feb 5, 2007 #5

    danago

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    Gold Member

    ok thats good to hear :) Thanks for the help
     
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