A person pushes on a mower...?

[justinbaker]

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

[Leong]

Since the mover moves in the horizontal direction only, we will consider the x-components only. Left direction : Negative; Right direction: Positive.

\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*}