Work
Definition
Work is done on an object by a constant
force moving the object through a distance
It is the product of the displacement and the
component of force parallel to the
displacement
Equation
W = F(//) x d
F
θ
d
W = Fdcosθ
Units
W=Fxd= Nm
1 N m = 1 joule (J)
Old British unit
1 J = .7376 ft lb
When Is There A Force and No
Work?
If object doesn’t move
If force is perpendicular to the displacement, like
carrying an object
 Cos θ = cos 90 = 0
 Force acting must have at least some
component in the same direction as
displacement
Example
A 50 kg crate is pulled 40 m along a
horizontal floor by a constant force of
100 N which acts at an angle of 37° with the
floor. The floor exerts a friction force of
50 N. Determine the work done by each
force on the crate, and the net work done.
Example 2
a) Determine the work a hiker must do on a
15.0 kg backpack to carry it up a hill of a
height of 10.0 m. Also determine b) the
work done by gravity on the backpack and
c) the net work done on the backpack