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Physics 1.1 - Unit 5 - Work, Power, Energy

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Angela Forlizzi

on 10 August 2016

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Transcript of Physics 1.1 - Unit 5 - Work, Power, Energy

Physics 1.1 - Unit 5 - Work, Power, Energy
Work
W = Fd

work = force x displacement

work is done when components of force are parallel to a displacement


ELASTIC PE
the PE in a stretched or compressed
elastic object



k = spring constant or force constant
flexible spring = small #
stiff spring = large #

x = distance compressed or stretched

Units will be N/m
PRACTICE
pg. 185, sample problem 5E

pg. 186, PRACTICE 5E #3
POWER
rate at which energy is transferred

P = W/t
Power = Work/Change in Time

Substitute definition of work

P = (F*d)/t
Power = work done over change in time
Alternative...
P = FV

Power = force x speed (or velocity)

Unit is watt (W)
Equal to 1 J/s

1 horsepower = 746 W
ME = KE + sum of PE


In absence of friction, total ME is conserved

MEi = MEf

MECHANICAL ENERGY
Work-KE Theorem
net work done is =
to the change in KE

Wnet = KE

Wfriction = ME

if no friction, ME = o
so...
MEi = MEf
KINETIC ENERGY
energy of object due to motion



Kinetic Energy = 1/2 x mass x velocity^2

PRACTICE 5B, pg. 173, #1-2
POTENTIAL ENERGY
energy of object due
to the position

Gravitational PE
PEg = mgh
Gravitational PE = mass x free fall accel x height
NET WORK
Wnet = Fnetd(cosangle)

Net work = net force displacement x cosine angle btwn them

Units are N*m or J

+ when force is in same direction as displacement

- when force is opposite displacement
PRACTICE 5A, pg. 170
PRACTICE 5F
Pg. 188, #1-2
when force applied at an angle -
only HORIZONTAL component does work

W = Fd(cosangle)
work = force x displacement x cosine angle
PRACTICE 5C
pg. 177, #2, 4
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