Flashcards in Energy Deck (37):
Write down the correct answer to complete the statement.
Energy can not…
be transferred from one source to another.
be created or destroyed.
travel along a pathway to another store.
Be created or destoryed
Describes the main change in energy stores for a coal fired power station.
a. Name the energy sources for:
i Input energy
ii Useful output energy
iii Wasted output energy.
Electrostatic (Electric current)
Thermal (Waste heat)
In one hour, coal supplies 500 000 J of energy. The wasted energy amounts to 380 000 J.
Calculate how much useful energy is produced in one hour.
500 000 – 380 000 = 120 000 J
When a football is kicked it gains kinetic energy.
What is the formula used to calculate kinetic energy?
Ek = ½ m v2
The football has a mass of 0.4 kg. When the football is kicked, it has a velocity of 15 m/s.
Calculate the kinetic energy of the moving football?
Ek = ½ x 0.4 x 152
Ek = 45 J
The un-stretched spring opposite has a length of 0.5 m but after a mass is added it is 0.6 m long.If the spring constant is 800 N/m.Calculate the stored elastic potential energy.
Ee = ½ k e2
extension of spring = 0.6 – 0.5 = 0.1 m
Ee = ½ x 800 x 0.12
Stored elastic potential energy of the spring = 4 J
A pole vaulter just clears the bar which is 5.1 m high. His mass is 62 kg. (g = 10N/kg)
What type of stored energy does he have as he just clears the bar?
gravitational potential energy
Work out how much stored energy the pole vaulter has due to his position above the ground.
GPE = m g h = 62 x 10 x 5.1 = 3162 J
As he falls back to the ground, this energy store will be
transferred into a new energy store. Name this new energy store.
When he lands, what happens to the energy stores described
dissipated as heat and sound
When a bowl of water and a stone are left in hot sunshine, the stone feels much hotter than the water. Which one has the highest specific heat capacity? Explain your answer.
The water has a higher heat capacity as it takes more heat energy to raise its temperature to that of the stone
Give two alternative units of power?
Joules/second or Watts
A blowtorch burns butane gas to heat metal pipes. Describe the energy transfers which occur as it is used.
energy is transferred into
energy usefully and
energy is wasted.
Explain how some of the transferred energy is wasted.
As thermal energy to the environment
The blowtorch transfers 2 kJ of energy in 4 mins. Work out the power of the blowtorch?
Power = energy transferred / time = 2000 / 240
Power of the blowtorch = 8.33Watts
Two cranes are lifting the same load of 120 kg to a height of 15 m
Crane A takes 30 s to lift the load. Crane B lifts the same load in 9 s.
Calculate the difference in power of the two cranes.
Crane A power = 1200 x 15 / 30 = 600W
Crane B power = 1200 x 15 / 9 = 2000W
Difference in power = 2000 – 600 = 1400 Watts
Storage heaters contain bricks which warm up and store the heat energy.
The bricks in this heater have a mass of 40 kg and are heated from 18 oC to 40 oC.If the specific heat capacity of the brick material is 850 J/kg oC.
Calculate the change in thermal energy during heating.
Change in thermal energy = Mass x Specific Heat Capacity x Temperature Change
ΔE = m x c x Δθ
temperature change Δθ = 40 – 18 = 22 oC change in thermal energy ΔE = 40 x 850 x 22
ΔE = 748 000 J or 748 kJ
The energy transfer diagram for a mobile phone shows that 100 J of electrical energy produces 45 J of light energy and 36 J of sound energy.
How much thermal energy will be dissipated by the phone?
45 J + 36 J = 81 J
100 J – 81 J = 19 J
19 J of thermal energy will be dissipated
Describe how the thermal energy produced by a bus driving along a road is dissipated.
The thermal energy increases the kinetic energy of the air particles therefore warming up the surroundings.
State why the total energy supplied an electric fan must always equal the total energy transferred by the electric fan.
Energy cannot be created or destroyed so:
total energy in = total energy out
The diagrams show two different types of loft insulation.
Fiberglass insulation Wool insulation
The wool needs to be thicker to have the same insulating properties. Explain which material has the highest thermal conductivity?
Wool has the highest thermal conductivity as it lets thermal energy through at a faster rate so a thicker layer is needed for the same insulation as the fiberglass.
Explain how trapped air reduces the rate of heat loss, in terms of thermal conductivity.
The air trapped inside the fiberglass acts as an insulator because air has a very low thermal conductivity and thermal energy can not pass through it easily.
The diagram represents the energy store transfers when a motor is lifting a weight.
How much electrical energy is transferred to a thermal energy store?
340 – (100 + 80) = 160 J
What is the total amount of dissipated energy?
160 + 80 = 240 J
Calculate the efficiency the of the useful energy transfer
Efficiency = useful output energy transferred = 100 = 0.294
total energy transfer input 340
The motor for a lift in a tall building uses 12 000 W of power. The lift and its passengers has a mass of 500 kg. The lift motor takes 10 s to raise the lift and its passengers through a height of 20 m.
Work out the percentage efficiency of the lift motor.
Efficiency = power out x 100 Power out = work work = force x distance
power in time
Power out = 5000 N x 20 m = 10 000 W Efficiency = 10 000 x 100 = 83 %
What is a fossil fuel?
A fuel formed in the geological past from the remains of living organisms.
What is a renewable energy source?
An energy source that can be replenished as it is used.
Why are fossil fuels considered to be a more reliable energy resource than renewable energy resources?
Produce a consistent energy supply with no gaps in energy delivery.
Despite a large investment by the UK government in wind power,the amount of fossil fuel used has not seen a decline. Give a possible explanation for this.
UK is using more energy and wind power can not meet this rise in demand.
The UK government is committed to investing in a "blend" of energy supply types to provide the UK’s energy needs for the next 100 years. Give an advantage of this rather than using just coal.
Evens out any variations in supply or cost of the energy source.Using only coal, if supplies stopped or the cost went up greatly,this would have a great impact on the consumer.
The graph shows the world use of renewable energies over the past sixty years.
Why has the use of wood increased very little over this time?
Limited supplies of wood and it takes a long time to grow new supplies. Also, pressure and legislation to prevent many trees from being cut down.
A lot of money has been invested in wind turbines. Why does this energy source not produce as much as any other renewable resource?
Each wind turbine only produces a small amount of electricity and not enough have been installed to match production from other renewable resources.
Describe how human activities have contributed to the greenhouse effect?
Burning fossil fuels for heating, transport and industry has led to a build up of carbon dioxide in the atmosphere (along with other greenhouse gases).
Explain how burning coal in power stations contributes to global warming.
Carbon dioxide produced. Carbon dioxide absorbs and reflects infrared radiation leading to additional warming.
Describe two problems associated with the storage of waste from nuclear power stations.
Waste is radioactive can cause cells to mutate.
Radioactivity lasts for thousands of years so needs long term storage.