WORK
Work is defined as the product of the
applied force and the displacement
through which that force is exerted.
W=Fs
WORK
Displacement
FORCE
• Question
– A sailor pulls a boat 30
m along a dock using a
rope that makes a 25o
angle with the
horizontal. How much
work does the sailor do
on the boat if he exerts
a force of 225 N on the
rope?
• How-To
– Draw a vector diagram
showing the force and
its components in the
direction of the
displacement. (Break
into X and Y
Components
Remember , work only
Occurs along x
component.
• Calculations
F
25o
d
• Givens
• F = 225 N
d = 30 m
Θ = 25o
W = Fd cosθ
W = (225N)(30m)(cos25o)
W = 6117.6 J
Power is defined as
work done divided
by the time used to
do the work.
P = Fd/t
The SI unit for power is
the joule/sec (or watt).
A machine is capable of a
power output of 1,000 watts.
How far can it lift a 50N
weight in 3 seconds?
HINT: Solve formula for “d”
= 60 meters
How much work is done holding a 1,200 N
piano at shoulder height for 15 minutes (your
shoulder is 1.5m above the ground)?
NONE
What if we lifted the piano 1m over that time?
1,200 J
How much power was exerted?
1.3 Watts