# Work and Energy Question

## Homework Statement

A person starts to mow a lawn with 50kg old fashioned push lawn mower. The handle of the mower makes an angle of 45 degrees with the sure of the lawn. A 200 N force is applied along the handle of the mower by the person
a. Determine the normal force exerted by the ground on the mower
b. If u=0.2, determine if the mower moves with a constant speed.
c.How far the mower will travel if the person pushes it for 1min along the staright line?

## The Attempt at a Solution

a) Fnormal = 200Nsin45 = 141

b) F=uFnormal (.2)(141) = 28.2
141-28.2
=112.8
F = ma
112 / 50
a = 2.24
c. ?

Not sure if a or b are correct

## Answers and Replies

Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
a) Fnormal = 200Nsin45 = 141

This (with a unit added in the end) is only accounting for the force necessary to counteract the push that the person exerts on the handle. The lawnmower also has a weight (assuming non-zero gravity).

SteamKing
Staff Emeritus
Science Advisor
Homework Helper

## Homework Statement

A person starts to mow a lawn with 50kg old fashioned push lawn mower. The handle of the mower makes an angle of 45 degrees with the sure of the lawn. A 200 N force is applied along the handle of the mower by the person
a. Determine the normal force exerted by the ground on the mower
b. If u=0.2, determine if the mower moves with a constant speed.
c.How far the mower will travel if the person pushes it for 1min along the staright line?

## The Attempt at a Solution

a) Fnormal = 200Nsin45 = 141

Is this the only force applied to the ground by the mower?

b) F=uFnormal (.2)(141) = 28.2
141-28.2
=112.8
F = ma
112 / 50
a = 2.24
c. ?

Not sure if a or b are correct

a. Determine the normal force exerted by the ground on the mower
You have the vertical component of the applied force + the weight [Mg] , so what is Fn.
b. If u=0.2, determine if the mower moves with a constant speed.
Use Newton Second Law
$$F_{net}=Ma$$
Think about the net force , what will it be?
Note that there is no motion along the y-axis and don't forget to take the frication into account.
What is your equation along the x-axis?
c.How far the mower will travel if the person pushes it for 1min along the staright line?
Use the linear motion laws [after getting 'a' from the previous part ]