Download work - Verona Public Schools

Do Now – 5 Minutes
Topic – Work / Kinetic Energy
Take out your Hooke’s Law Lab – I will collect
it.
A shopper in a supermarket pushes a cart with
a force of 35 N downward at an angle of 25°.
Find the work done by the shopper on the cart
as the shopper moved along a 50 m length of
aisle.
NOTE: Only the force in the x-direction
contributes to moving the cart. Use only the
x-component of the force!
Homework
Hooke’s Law Lab - Due today
Friction Lab (Four Days Late)
Recap
What was the new concept we learned
about yesterday?
What was its formula?
What are its units?
What is an example of work being done?
Formula for Work
The formula for Work is:
W=F•d
Work = Net Force • Displacement
[J]
[N]
[m]
W
F d
What is Work?
Note: Work is considered positive if
the displacement is in the SAME
direction as the force.
What force would make negative
work?
Based on our Do Now – what is the
work required to move our box from the
beginning of the class?
Examples of Work
When I hold a book outwards like so –
am I doing work?
Why or why not?
When I push a cart at constant velocity –
am I doing work?
Why or why not?
Examples of Work
Although I am holding the book, and it is
tiring, and I feel like I am exerting a force,
is the book moving?
Since there is no displacement, work is
zero.
Examples of Work
Force is equal to mass • acceleration.
If the object is moving at a constant
velocity, then there is no work being
done.
Examples of Work
A weight lifter lifts a set of weights a
vertical distance of 1.55 m.
If a constant net force of 350 N is exerted
on the weights, what is the net work done
on the weights?
Examples of Work
If 3 J of work is done to raise a 600 g
pineapple, how far is the pineapple lifted?
(Remember – 1,000 g = 1 kg)
Examples of Work
Mr. Fineman’s classroom cart starts off at
rest. Mr. Fineman pushes the 4.5 kg cart with
a force of 2.25 N for the span of 3 seconds.
What is the resulting acceleration of the cart?
What is the displacement of the cart over this
period of time?
What work did Mr. Fineman do over this time?
What is the final velocity of the cart after all of
this?
“Ugh… Mr. Fineman”
Wasn’t that a pain to figure out?
Fortunately, using logic and reasoning
(and Physics formulas) we can figure out
how fast objects will move.
What does the law of Conservation of
Energy say?
Energy cannot be created nor destroyed
“Ugh… Mr. Fineman”
When you do work to an object, what are
you doing to it?
Giving the object energy!
That energy now goes into making the
object move.
Kinetic Energy
The energy associated with an object
moving is known as kinetic energy.
An object’s kinetic energy is dependent
on the mass of the object, as well as how
fast the object is moving.
The heavier and faster the object, the
more kinetic energy it has.
Formula for Kinetic Energy
The formula for Kinetic Energy is:
భ
మ
KE = • m • v2
Work = Net Force • Displacement
[J]
[N]
[m]
W
F d