Work and Power Equations
Copy these equations down
Work is the product of the force applied and the
displacement.
Note:
1. the force has to be in the direction of motion (or at
least have a component in the direction of motion)
2. there has to actually be motion
Basic Equation:
W= Fd
W is for work measured in joules
F is for force measured in newtons
d is for displacement measured in meters
A Joule is equal to a Newton-meter
J= Nm
Examples of work being done:
1. Sydney pushing a box across the floor. W=Fd
2. Leighton picking up an elephant. W=Fd (but F in
this case is mg)
When is angle important?
Sydney pulls Tucker in a wagon a distance of 10 m
with a force of 30 N along a handle that is 20 with
the horizontal. In this case the direction of force is at
an angle of 20 with the direction of displacement.
Therefore, we need to calculate the component of the
30 N force that is be used in work by using this
equation: W=Fdcos
What about this?
20 m
3m
Josh pushes a box up the 30 incline which is 20 m
long and 3 m high with an effort force of 15 N. How
much work did he do?
F = 15 N. The distance of importance is the distance
that is parallel to the direction of force…the 20 m.
Since the 15 N force is in the exact same direction as
the 20 m distance, nothing else is important.
Power describes how fast work is
being done.
P= W/t or P= Fd/t
P is for power measured in Watts. W is for work measured in
Joules. t is for time measured in seconds. A watt is equal to a
joule per second.
1 W= J/s
W is confusing??? If you see it in an equation, it stands for
Work. If you see it behind a number, it stands for watts.
Assignment:
Practice Problems 1-12 throughout
chapter 10.
(Pages 227, 229, and 231)
A4 only, go to next slide
On Wednesday, you will be having a
quiz over the assignment given in
class last class (conservation of
momentum)
If you have not completed that assignment or do not
know what it is, check the diary and get it done at home.
Today in class, you need to quietly work on the
assignment given.
Keep in mind, your grade is what you earn. Good grades
do not fall from the sky. Make sure you are spending
time at home working on physics assignments. Also,
watch for video links that I will be placing on my website
to help with conservation of momentum problems.