http://www.ck12.org Chapter 4. Motion and Forces
Work = 100 N×200 m = 20,000 N • m
Notice that the unit for work in the answer is the Newton • meter (N • m). This is the SI unit for work, also called
thejoule (J). One joule equals the amount of work that is done when 1 N of force moves an object over a distance
of 1 m.
Q: After Clarissa mows her grandmother’s lawn, she volunteers to mow a neighbor’s lawn as well. If she pushes the
mower with the same force as before and moves it over a total of 234 meters, how much work does she do mowing
the neighbor’s lawn?
A: The work Clarissa does can be calculated as:
Work = 100 N×234 m = 23,400 N • m, or 23,400 J
Calculating Force or Distance When Work Is Known
The work equation given above can be rearranged to find force or distance if the other variables are known:
Force=DistanceWork
Distance=WorkForce
After Clarissa finishes mowing both lawns, she pushes the lawn mower down the sidewalk to her own house. If
she pushes the mower over a distance of 30 meters and does 2700 joules of work, how much force does she use?
Substitute the known values into the equation for force:
Force=^270030 mJ=90 N
Q: When Clarissa gets back to her house, she hangs the 200-Newton lawn mower on some hooks in the garage (see
theFigure4.72). To lift the mower, she does 400 joules of work. How far does she lift the mower to hang it?
A: Substitute the known values into the equation for distance:
FIGURE 4.72
Summary
- Work can be calculated with the equation: Work = Force×Distance.