The problems are on the forms of energy worksheet. Try them on your own first, then compare with the answers below.
Quick answer: Energy is the ability to make things change, and it is measured in joules (J). These worked answers correct the 20 problems of the grade 6 science worksheet on forms of energy, from name the form to food energy on a ride: each solution shows the formula, the substitution and the final answer with its unit.
Each answer gives the form of energy, the calculation and the result with its unit in bold. Check that your energy chains show every stage and that your percentages are worked out from useful energy divided by total energy.
Level: Grade 6 science (Year 7 · Class 6) · Curriculum: MS-PS3
Problem 1 Name the form
1. Kinetic.2. Thermal.
3. Light.
4. Electrical.
5. Chemical (stored in the food).
Problem 2 Joules
1. The joule, J.2. 2.5 × 1000 = 2500 J.
3. 4000 ÷ 1000 = 4 kJ.
Problem 3 Renewable or not?
Renewable: wind, biogas, sunlight.Non-renewable: coal, natural gas, oil.
Problem 4 A battery fan
1. Chemical energy.2. Electrical energy.
3. Kinetic energy (moving blades and air).
Problem 5 Wind turbine chain
1. A: kinetic (moving air).2. B: kinetic (spinning blades).
3. C: electrical.
4. D: light (with some thermal energy as waste).
Problem 6 Law of conservation
1. Energy cannot be created or destroyed, only transferred or transformed.2. The chemical energy was transformed into light and thermal energy (mostly thermal), which spread into the surroundings. It did not disappear.
Problem 7 Wasted energy of a lamp
1. 60 − 6 = 54 J.2. It is thermal energy (the bulb gets hot).
Problem 8 Useful percentage
1. Filament: 10 ÷ 100 × 100 = 10 %. LED: 8 ÷ 10 × 100 = 80 %.2. The LED lamp wastes less (20 % compared with 90 %).
Problem 9 Comparing appliances
1. Kettle 100 J, charger 10 J, motor 50 J.2. Kettle 900 ÷ 1000 = 90 %; charger 40 ÷ 50 = 80 %; motor 150 ÷ 200 = 75 %.
3. The electric kettle (90 %).
Problem 10 More kinetic energy
1. At 10 m/s: faster means more kinetic energy.2. The truck has more kinetic energy because it has a much greater mass at the same speed.
Problem 11 Bicycle dynamo
1. Chemical (food) → kinetic (pedals and dynamo) → electrical → light (and thermal).2. Pedalling faster gives the dynamo more kinetic energy each second, so more electrical energy reaches the lamp and it gives out more light.
Problem 12 Motorbike engine
1. 200 − 50 = 150 J.2. 50 ÷ 200 × 100 = 25 %.
3. It spreads into the surroundings (air and the engine parts get hot) and cannot be used again.
Problem 13 Sources of electricity
1. 30 + 15 + 5 + 35 + 15 = 100 units.2. Renewable = hydro + wind + solar = 50 units, so 50 ÷ 100 × 100 = 50 %.
3. Coal (or natural gas).
Problem 14 Spot the error
1. Energy cannot be created, so a panel cannot make energy from nothing.2. A solar panel transforms light energy from the Sun into electrical energy.
Problem 15 Solar charger
1. 4 ÷ 20 × 100 = 20 %.2. 4 × 60 = 240 J.
Problem 16 Two-stage chain
1. 80 % of 40 J = 0.80 × 40 = 32 J.2. 32 ÷ 100 × 100 = 32 %.
3. 100 − 32 = 68 J (60 J at the power station and 8 J in the lamp).
Problem 17 Saving energy with LEDs
1. 6 ÷ 7.5 × 100 = 80 %.2. Filament: 60 × 3600 = 216 000 J = 216 kJ. LED: 7.5 × 3600 = 27 000 J = 27 kJ.
3. 216 − 27 = 189 kJ saved.
Problem 18 Missing energy in a phone
1. x = 100 − 25 − 5 = 70 J.2. (25 + 5) ÷ 100 × 100 = 30 %.
3. 70 % of the energy is transformed into thermal energy, which warms the phone and the air around it.
Problem 19 Power for a farm
1. Solar panels are a good choice: sunshine is plentiful and free, and there is no fuel to buy or carry. Solar is renewable and makes no smoke, while diesel is non-renewable and wind is too weak.2. Store energy in batteries during the day: the chemical energy in the batteries is transformed back into electrical energy for the lamps at night.
Problem 20 Food energy on a ride
1. 25 % of 400 = 0.25 × 400 = 100 kJ.2. 400 − 100 = 300 kJ.
3. 500 ÷ 100 = 5 bananas.
