Module 3.3 - Work, Energy and Power Flashcards
What is work done?
The energy transferred
How do you work out work done, w?
Work done = force x distance
W = f x d
How do you work out work done when a mass is given?
W = mg x d
How do you work out work done at an angle?
W = f x cos(theta) x d
At what angle is there no work done and why ?
90˚ as cos(90) = 0
What is a closed system?
Any system where every transfer of energy is accounted for
What is a joule?
> Unit of energy - J
Equivalent to one Nm
One joule of work is transferred when a force of 1N causes an object to move a distance of 1m
What is the principle of conservation of energy?
States that the total energy of a closed system remains CONSTANT. Energy cannot leave or enter the system.
What are the two forms of energy?
> Transfer
> Conservation
What are the nine types of energy stores?
> Kinetic > Thermal > Nuclear > Chemical > Internal > Gravitational > Elastic > Electrostatic > Magnetic
Where are kinetic energy stores found?
In a moving object
Where are thermal energy stores found?
In a warm object
Where are gravitational energy stores found?
In a lifted object
Where are elastic energy stores found?
e.g. stretched or compressed spring
Where are chemical energy stores found?
Between atoms and molecules that could react
Where are magnetic energy stores found?
In two separate magnets that are attracting or repelling
Where are electrostatic energy stores found?
In two separated electric charges that
are attracting or repelling
Where are nuclear energy stores found?
Released through radioactive decay: fusion or fission
What are the 4 methods of energy transfer?
> Mechanically
Electrically
By heating
By radiation
How is energy transferred mechanically?
When a force MOVES an objects (work is done)
How is energy transferred electrically?
When a charge moves through a potential difference
How is energy transferred by heating?
When energy moves from a hotter object to a cooler object
How is energy transferred by radiation?
e.g. microwaves, visible light. x-rays (often called light energy)
Define Gravitational potential energy
Energy that an object has due to its POSITION
How do you work out Gravitational potential energy, Ep?
Ep = mgh
Ep - J
m - kg
g - N/kg
h - m
What is kinetic energy?
Energy gained as it is ACCELERATED by a force
How do you work out kinetic energy of an object, Ek?
Ek = 1/2mv^2
Ek - J
m - Kg
v - m/s
What happen to Ep as Ek increases?
Ep decreases
What happens to Ek as Ep increases?
Ek decreases
Define power
The rate of doing work
What is a watt?
> Unit of power
> Joules per second
How do you work out power in terms of energy?
P = W ÷ t
P - W
W - J
t - s
What is 1kW equivalent to?
1000W
How do you work out energy using power?
E = P x t
How do you work out power using velocity?
P = Fv
P - W
F - N
v - m/s
How do you work out the effiency of a mechanical system?
(Useful energy output ÷ Total energy input) x 100
