#### 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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