# A person pushes on a mower ?

1. Sep 20, 2004

### 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

2. Sep 20, 2004

### Leong

Since the mover moves in the horizontal direction only, we will consider the x-components only. Left direction : Negative; Right direction: Positive.
$$\begin{multline*} \begin{split} &Newton's\ 2nd\ Law:\\ &\sum \vec{F}=m\vec{a}\\ &\vec{F_x}+\vec{D}=m\vec{a}\\ &|\vec{F}|cos46^0 + (-49.3)=17.0*(\frac{1.1-0}{2.0})\\ &|\vec{F}|=84.4\ N\\ \end{split} \end{multline*}$$

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