Energy resources worksheet answers for grade 8 science (free PDF download)

Problem 1 Renewable or not

1. Renewable: wind, tidal, biomass. Non-renewable: coal, uranium, natural gas.
2. The fossil fuels in the list are coal and natural gas.

Problem 2 How fossil fuels formed

1. They formed from the remains of ancient plants and animals.
2. It took millions of years.
3. We use them much faster than they form, so they will eventually run out.

Problem 3 Stages of a power station

1. A is the fuel, B the boiler, C the turbine, D the generator and E the grid (electricity).
2. The turbine is turned by steam.

Problem 4 Good and bad points

1. Wind: wind.
2. Nuclear: nuclear.
3. Solar: solar.
4. Coal: coal.

Problem 5 Greenhouse gases

1. Carbon dioxide and methane.
2. Carbon dioxide (CO₂).
3. They absorb it and send some of it back towards the ground.

Problem 6 Simple efficiency

1. Efficiency = useful output ÷ total input × 100.
2. 40 ÷ 200 × 100 = 20 %.
3. 200 − 40 = 160 J wasted.

Problem 7 Power station efficiency

1. Efficiency = 840 ÷ 2400 × 100 = 35 %.
2. 2400 − 840 = 1560 MJ.
3. It goes to the surroundings as heat, for example from the cooling towers and flue gases.

Problem 8 Energy from a wind turbine

1. 2.0 MW = 2000 kW.
2. E = P × t = 2000 × 5.0 = 10 000 kWh.
3. 10 000 ÷ 10 = 1000 homes.

Problem 9 Reading a Sankey diagram

1. The useful band is half of the input: 50 units.
2. 100 − 50 = 50 units wasted.
3. 50 ÷ 100 × 100 = 50 %.
4. Gas: 0.50 × 1000 = 500 MJ. Coal: 0.35 × 1000 = 350 MJ. The gas station gives 150 MJ more.

Problem 10 Solar panels at home

1. 20 × $0.15 = $3.00 a day.
2. 30 × $3.00 = $90.
3. $3600 ÷ $90 = 40 months.

Problem 11 Carbon dioxide from two fuels

1. 300 × 0.90 = 270 kg.
2. 300 × 0.40 = 120 kg.
3. 270 − 120 = 150 kg less with gas.

Problem 12 Wind and solar limits

1. Solar panels give no output in darkness, and wind may be low at night.
2. Both resources depend on the weather, so output may fall at the same time.
3. Batteries or backup stations (such as hydroelectric or gas) can cover the gap.

Problem 13 Greenhouse diagram

1. A is sunlight (visible light) and B is infrared from the ground.
2. C is the layer of greenhouse gases.
3. D is infrared sent back down to the ground.
4. Arrow D gets larger.

Problem 14 Spot the errors

1. Uranium is not burned. Its atoms are split in nuclear fission, which releases the heat.
2. Global warming is caused by extra greenhouse gases trapping infrared. The ozone layer blocks ultraviolet.

Problem 15 Carbon dioxide in the air

1. 413 − 317 = 96 ppm.
2. 96 ÷ 317 × 100 = 30.3 %, so 30 %.
3. 1960-1980: 22 ppm in two decades, which is 11 ppm per decade. 2000-2020: 44 ppm in two decades, which is 22 ppm per decade. The rate has doubled.

Problem 16 Hydroelectric dam

1. E = m g h = 5.0 × 10⁶ × 9.8 × 80 = 3.92 × 10⁹ J = 3.9 × 10⁹ J.
2. 0.85 × 3.92 × 10⁹ = 3.33 × 10⁹ J, which is 3.3 × 10⁹ J.
3. 3.33 × 10⁹ ÷ 3.6 × 10⁶ = 926 kWh.

Problem 17 A wind farm

1. Rated power = 20 × 3.0 = 60 MW, so average = 0.30 × 60 = 18 MW.
2. E = 18 × 8760 = 157 680 MWh, or 1.6 × 10⁵ MWh.
3. 157 680 MWh = 157 680 000 kWh, and 157 680 000 ÷ 4000 = 39 420, so about 39 000 homes.

Problem 18 Uranium and coal

1. 8.0 × 10¹³ ÷ 2.4 × 10⁷ = 3.3 × 10⁶ times.
2. The mass is 3.3 × 10⁶ kg, which is 3300 tonnes.
3. Reasons include radioactive waste, high building cost and the risk of accidents.

Problem 19 Choosing power for a village

1. Diesel: fuel must be bought and delivered, it releases CO₂, but it works on demand. Solar with batteries: no fuel costs and no CO₂ in use, works in the sunny climate, but batteries are expensive and need replacing. Small hydro: very cheap to run but fails in the dry season.
2. Solar with batteries is the best choice, because sunshine is plentiful and reliable, there is no fuel to transport and the village produces no CO₂. A small generator could be kept as backup.

Problem 20 Forest and fossil fuel

1. 40 000 × 0.90 = 36 000 kg.
2. Area = 36 000 ÷ 1.0 = 36 000 m².
3. 36 000 ÷ 10 000 = 3.6 hectares.