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Homework Help: A person pushes on a mower ?

  1. Sep 20, 2004 #1
    Here is the question i have. I got the first two no prob. But ihave no idea how i got the third answer. The answers shown are all correct. So if anyone can explain how to get the third answer, thanks everyone

    A person pushes a 17.0 kg lawn mower at constant speed with a force of 71.0 N directed along the handle, which is at an angle of = 46.0° to the horizontal

    http://www.webassign.net/giancoli5/4_40alt.gif

    Calculate the horizontal retarding force on the mower = 49.3 N

    Calculate the normal force exerted vertically upward on the mower by the ground =218

    Calculate the force the person must exert on the lawn mower to accelerate it from rest to 1.1 m/s in 2.0 seconds (assuming the same retarding force).
    =82.8


    Thanks,
    justinbaker@gmail.com
     
  2. jcsd
  3. Sep 20, 2004 #2
    Since the mover moves in the horizontal direction only, we will consider the x-components only. Left direction : Negative; Right direction: Positive.
    [tex]
    \begin{multline*}
    \begin{split}
    &Newton's\ 2nd\ Law:\\
    &\sum \vec{F}=m\vec{a}\\
    &\vec{F_x}+\vec{D}=m\vec{a}\\
    &|\vec{F}|cos46^0 + (-49.3)=17.0*(\frac{1.1-0}{2.0})\\
    &|\vec{F}|=84.4\ N\\
    \end{split}
    \end{multline*}
    [/tex]
     

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