energy

Question 1

what is energy

Answer 1

energy is required for things to work

Question 2

what is an energy store

Answer 2

energy stores are ways in which energy can be stored in a system
e.g. food and fossil fuels are chemical potential stores.
a book on a tall shelf is a gravitational potential store
a bullet is a kinetic store

Question 2

7 types of energy

Answer 2

Nuclear
Internal
Chemical potential
Elastic potential
Kinetic
Gravitational potential
Elastic potential
NICEE KG

Question 2

what is the SI unit for energy

Answer 2

Joule (J)

Question 3

what determines more energy in a kinetic store

Answer 3

objects moving at higher speeds have more energy in the kinetic store

Question 4

what determines more energy in a gravitational potential store

Answer 4

objects further from the ground have more energy in the gravitational potential store

Question 4

what determines more energy in a elastic potential store

Answer 4

elastic objects being strecthed or compressed have energy in the elastic potential store

Question 5

what determines more energy in a chemical potential store

Answer 5

chemical bonds have energy in the chemical potential store

Question 6

what determines more energy in a internal store

Answer 6

objects of higher temperature have more energy in the internal store

Question 7

what determines more energy in a nuclear store

Answer 7

nuclei in atoms have energy in the nuclear store

Question 7

4 ways energy can be transferred from one energy store to another in four different pathways

Answer 7

1. mechanically (by a force acting over a distance)
2. by heating (as a result of a temperature difference)
3. by propagation of waves (both electromagnetic and mechanical)
4. electrically (by charges moving through a potential difference)

Question 7

what form of energy transfer is this?
energy is transferred from a cup of hot tea to a spoon when the spoon is placed in it

Answer 7

heating

Question 7

what form of energy transfer is this?
Energy is transferred from an athlete to a set of weights when she does work in exerting a force to lift them above her head

Answer 7

work done by a force

Question 8

what form of energy transfer is this?
energy is transferred from a light bulb to the surroundings by electromagnetic waves(light)

Answer 8

waves

Question 9

what form of energy transfer is this?
energy is transferred from an electric cell to a light bulb by an electriccurrent

Answer 9

electric current

Question 9

what is the principle of conservation of energy

Answer 9

the principle of conservation of energy states that energy cannot be created or destroyed. Energy can be transferred from one store to another. The total energy of an isolated system is constant

Question 10

isolated system meaning

Answer 10

no transfer of energy and matter in/out of the system (ie no interaction with its surroundings

Question 10

Kinetic energy formula

Answer 10

Ek = 1/2mv^2
where
Ek = energy in the kinetic store (J)
m = mass of body (kg)
v = speed of the body (m/s)

Question 11

work done by a force formula

Answer 11

W = Fs
where
W = work done by a constant force F (J)
F = constant force (N)
s = distance moved in the direction of the force (m)

Question 11

potential energy formula

Answer 11

Ep = mgh
where
Ep = energy in the GP store
m = mass of the body (kg)
g = gravitational field strength (N/kg)(9.8)
h = height (m)

Question 11

work done against gravity formula

Answer 11

W = F x h = mgh
(F = mg)
work done against against gravitational force = GPE

Question 12

power definition

Answer 12

power is defined as the work done or energy transferred per unit time.

Question 12

power SI unit

Answer 12

watt(W)

Question 12

power formula

Answer 12

P = W/t =E/t
where
P = power(W)
W = work done(J)
E = energy transferred (J)
t = time taken (s)

Question 13

one watt (W) definition

Answer 13

one watt (W) is defined as the rate of work done or energy conversion of one joule per second.
one watt = one joule / one second
1W = 1J s^-1 = 1J/s

Question 14

concept of efficiency in an ideal machine

Answer 14

the total energy output is equal to its total energy input
in reality, the useful energy output of a machine is always less than the energy input

Question 14

efficiency formula

Answer 14

efficiency = Useful energy output/total energy input x 100%

Question 15

what are fossil fuels

Answer 15

fossil fuels have energy in the chemical potential stores.
when a fuel is burnt in air for cooking food, heat transfers from the chemical potential store of the fuel to the internal stores if the food and the surroundings

Question 16

advantages of fossil fuels

Answer 16

1. more reliable than other resources as fossil fuels do no depend on environmental factors
2. relatively cheaper cost of production compared to other resources

Question 17

disadvantages of fossil fuels

Answer 17

1. non renewable energy resource
2. environmental pollution from the gases produced during burning contributes to global warming