12 Physics - Energy Flashcards
State 1o types of energy
nuclear* kinetic chemical gravitational potential geothermal* thermal light (radiated) sound electrical elastic (stain)
what are the units of energy?
Joules (J)
what are the 2 main categories of energy an object can have?
energy in action
energy store
what type of energy does a moving object have?
kinetic
what type of energy would be found in a car that is stationary at the top of a hill?
gravitational potential
chemical (if the car has fuel in it)
what is work?
it is the force applied to an object to make it move a given distance
what is the unit of work?
Joules (J)
what is the equation for work done?
work done (J) = force (N) x distance
what is the equation for force?
force = mass (Kg) x acceleration (m/s^2)
what is the value for acceleration due to gravity?
10 N unless stated otherwise
a bag of 7 Kg is lifted onto your shoulder which is 1.5m high
how much work have you done?
f = mass x acceleration f = 7 x 9.8 f = 68.6 J
w = f x d w = 68.8 x 1.5 w = 102.9 J
James Bond falls out of a plane which is 30km high, he weights 75kg
what work was done to j. bond?
f = 75 x 9.8 f = 735 J
w = 735 x 30000
w = 22 050 000 J
= 22 050 KJ
state the principle of energy conservation
energy cannot be created or destroyed, it can only be transferred from one form to another
why is a machine never 100 % efficient?
because heat energy is lost
when energy is transformed, heat is always produced
a car moves due to a reaction in the engine that provides force
state all energy changes from petrol to the car parked at the top of a hill
the car starts with chemical energy stored in petrol
combustion happens and heat is produced
-sound, heat–> energy that is wasted
the car moves - kinetic energy
the car parks - gravitational potential
what is GPE?
gravitational potential energy
the amount of stored energy an object has based on the mass of an object, its height off the ground, and the amount of gravity
it is also the amount of work an object can do due to gravity
what is the equation for GPE
GPE (J) = mass (Kg) x gravitational force (N/KG) x height (m)
GPE = mgh
what is KE?
kinetic energy
energy associated with a moving object
it is dependent on the mass of the object and its velocity (speed in a given direction)
equation for KE
KE = 0.5 x mass x speed^2
what is the relationship between work done, GPE, and KE?
they are the same
work done = GPE = KE
what is power dependent on?
work done
time
what is the unit of power
Watts (W) or J/s (joules per second)
equation for power?
work done (J) or energy transformed
_________________________________
time (s)
equation for acceleration?
final velocity - initial velocity
______________________
time
a car accelerates to a speed of 10m/s in 5 seconds. It weighs 1000N
a) acceleration
b) work done?
c) power?
a) 10-0/5 = 2m/s^2
b) work = F x d
what is efficiency?
ratio of total energy input compared to how much useful energy is given out
equation
efficiency
useful energy output
_________________ x 100 =
total energy input
how is electricity generated using thermal methods
fuel is burnt or nuclear reactor release heat energy
the heat energy heats water in a boiler
steam comes out and moves turbines (rotation)
generator uses rotation to make electricity
what are advantages and disadvantages of the thermal method of generating electricity
advantages:
- if it is nuclear it does’t burn - no pollution
- generates lots of electricity when compare to other methods such as solar
disadvantages
- if it isn’t nuclear it burns and pollutes a lot
- it is non-renewable
- nuclear is dangerous and stays radioactive for years
what are alternative sources of electricity available?
what are adv. & disadv. of each?
solar, wind- produces little energy, only available largely in some places, wind is noisy and ugly. Renewable, no pollution
hydroelectric- building of dam harms ecosystem & is expensive, & can only be done in some places. renewable, no pollution
wave- difficult, only few devices were successful. Renewable, no pollution
geothermal- deep drilling is difficult and expensive. no pollution uses earths natural heat
biofuel- huge areas to grow plants, pollutes. Can regrow, renewable
what is the source of all renewable and un-renewable energy?
SUN
