12 Physics - Energy

Question 1

State 1o types of energy

Answer 1

nuclear*
kinetic
chemical
gravitational potential
geothermal*
thermal
light (radiated)
sound
electrical
elastic (stain)

Question 2

what are the units of energy?

Answer 2

Joules (J)

Question 3

what are the 2 main categories of energy an object can have?

Answer 3

energy in action

energy store

Question 4

what type of energy does a moving object have?

Answer 4

kinetic

Question 5

what type of energy would be found in a car that is stationary at the top of a hill?

Answer 5

gravitational potential

chemical (if the car has fuel in it)

Question 6

what is work?

Answer 6

it is the force applied to an object to make it move a given distance

Question 7

what is the unit of work?

Answer 7

Joules (J)

Question 8

what is the equation for work done?

Answer 8

work done (J) = force (N) x distance

Question 9

what is the equation for force?

Answer 9

force = mass (Kg) x acceleration (m/s^2)

Question 10

what is the value for acceleration due to gravity?

Answer 10

10 N unless stated otherwise

Question 11

a bag of 7 Kg is lifted onto your shoulder which is 1.5m high
how much work have you done?

Answer 11

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

Question 12

James Bond falls out of a plane which is 30km high, he weights 75kg
what work was done to j. bond?

Answer 12

f = 75 x 9.8
f = 735 J

w = 735 x 30000
w = 22 050 000 J
= 22 050 KJ

Question 13

state the principle of energy conservation

Answer 13

energy cannot be created or destroyed, it can only be transferred from one form to another

Question 14

why is a machine never 100 % efficient?

Answer 14

because heat energy is lost

when energy is transformed, heat is always produced

Question 15

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

Answer 15

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

Question 16

what is GPE?

Answer 16

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

Question 17

what is the equation for GPE

Answer 17

GPE (J) = mass (Kg) x gravitational force (N/KG) x height (m)

GPE = mgh

Question 18

what is KE?

Answer 18

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)

Question 19

equation for KE

Answer 19

KE = 0.5 x mass x speed^2

Question 20

what is the relationship between work done, GPE, and KE?

Answer 20

they are the same

work done = GPE = KE

Question 21

what is power dependent on?

Answer 21

work done

time

Question 22

what is the unit of power

Answer 22

Watts (W) or J/s (joules per second)

Question 23

equation for power?

Answer 23

work done (J) or energy transformed
_________________________________
time (s)

Question 24

equation for acceleration?

Answer 24

final velocity - initial velocity
______________________
time

Question 25

a car accelerates to a speed of 10m/s in 5 seconds. It weighs 1000N

a) acceleration
b) work done?
c) power?

Answer 25

a) 10-0/5 = 2m/s^2

b) work = F x d

Question 26

what is efficiency?

Answer 26

ratio of total energy input compared to how much useful energy is given out

Question 27

equation

efficiency

Answer 27

useful energy output
_________________ x 100 =
total energy input

Question 28

how is electricity generated using thermal methods

Answer 28

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

Question 29

what are advantages and disadvantages of the thermal method of generating electricity

Answer 29

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

Question 30

what are alternative sources of electricity available?

what are adv. & disadv. of each?

Answer 30

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

Question 31

what is the source of all renewable and un-renewable energy?

Answer 31

SUN