Work and Energy Physics Notes with Practice Problems

·

note that I horsepower up At highest point KE 0 =




is equivalent to 76W At lowest point U 0 =




when
buying electricity , you are
charged by the kilowatt-hour.



Section 6 .
1




potential energy is energy that is "stored" in an object by a force.

·
it is related to work by
VAB = -

WAB
·
we can define quavitational potential energy energy (GPE) as


AUgrav migh =




here , his change in height
This V; to value reference location where U = 0
is
change in
get at location
,
we need to choose a


arbitrary ; only Du , not v has physical meaning.


regardless of choice of where U 0 =
,
the changes inV between
heights are same

·
we choose a convenient location for U = 0 = U =0 ,
based on problem ·

* choose the lowest height.
·
For GPE horizontal ,
motion has no effect (no gravitational Force)

Section 6 2 .




·
if UA UB=
,
the
Wgvav , AB
=
0

this means that gravity is a conservative force ,
one for which work done

around is
a closed path displacement = o zero.


a nonconservative force does a non-zero amount of work on object that moves around a closed path
for a conservative force , path taken from point A to B doesnt matter ; only the endpoints
themselves matters.



Friction

Kinetic friction always acts opposite to the motion so angle between His displacement is 1800 ,
·




,



and Wp =
-fic(DX)
=> Wr + 0 around closed path , and ty is non-conservative .