GCSE Energy (Physics Paper 1) — Questions and Answers
Question 1: Which equation correctly gives the kinetic energy of a moving object?
- Ek = ½ × m × v² (Correct answer)
- Ek = m × g × h
- Ek = m × v
- Ek = ½ × m × v
Correct answer: Ek = ½ × m × v²
Kinetic energy = ½ × mass × (speed)². Doubling the speed quadruples the kinetic energy because of the squared term.
Kinetic energy is the energy an object has because it is moving. On the GCSE equation sheet it is written Ek = ½mv², with mass in kilograms, speed in metres per second and energy in joules. Because speed is squared, a car travelling at twice the speed has four times the kinetic energy, which is why stopping distances grow so quickly at higher speeds.
Question 2: A 2 kg mass is lifted 5 m vertically. Taking g = 9.8 N/kg, how much gravitational potential energy does it gain?
- 10 J
- 49 J
- 98 J (Correct answer)
- 196 J
Correct answer: 98 J
Ep = m × g × h = 2 × 9.8 × 5 = 98 J.
Gravitational potential energy stored when an object is raised is calculated with Ep = mgh, where m is mass (kg), g is the gravitational field strength (9.8 N/kg on Earth) and h is the height change (m). Substituting: 2 kg × 9.8 N/kg × 5 m = 98 J. The energy is transferred to the gravitational store and is released again if the object falls.
Question 3: Which of the following is NOT one of the energy stores used in the 9-1 GCSE specification?
- Thermal
- Elastic potential
- Sound (Correct answer)
- Magnetic
Correct answer: Sound
Sound is a way energy is transferred (by waves), not an energy store. The stores are kinetic, thermal, chemical, gravitational potential, elastic potential, nuclear, magnetic and electrostatic.
The current GCSE model describes energy as being held in stores and moved between them by transfer pathways. The eight stores are kinetic, thermal, chemical, gravitational potential, elastic potential, nuclear, magnetic and electrostatic. The four pathways are mechanical work, electrical work, heating, and radiation (including light and sound waves). So sound is a pathway, not a store.
Question 4: Which equation defines the efficiency of an energy transfer?
- Efficiency = total input energy ÷ useful output energy
- Efficiency = useful output energy ÷ total input energy (Correct answer)
- Efficiency = useful output energy × total input energy
- Efficiency = wasted energy ÷ useful output energy
Correct answer: Efficiency = useful output energy ÷ total input energy
Efficiency = useful output energy transfer ÷ total input energy transfer. It is a ratio between 0 and 1 (or 0% and 100%).
Efficiency compares how much of the energy put into a device ends up doing the useful job. It is calculated as useful output energy ÷ total input energy (or the same ratio using power). Because some energy is always dissipated, usually as heating of the surroundings, efficiency is always less than 1 (100%). For example, a motor that takes in 500 J and does 300 J of useful work has an efficiency of 0.6 or 60%.
Question 5: A kettle has a power rating of 2000 W. How much energy does it transfer in 3 minutes?
- 6,000 J
- 60,000 J
- 360,000 J (Correct answer)
- 666 J
Correct answer: 360,000 J
E = P × t = 2000 W × 180 s = 360,000 J. Time must be converted to seconds.
Power is the rate of energy transfer, so energy transferred = power × time (E = Pt). The power is 2000 W (2000 joules per second) and 3 minutes is 3 × 60 = 180 seconds. 2000 × 180 = 360,000 J, which can also be written as 360 kJ. A common mistake is to leave time in minutes, which gives an answer 60 times too small.
Question 6: Which of these is a non-renewable energy resource?
- Wind
- Natural gas (Correct answer)
- Hydroelectricity
- Solar
Correct answer: Natural gas
Natural gas is a fossil fuel and cannot be replenished on a human timescale, so it is non-renewable.
Renewable resources are those that are replenished as they are used, such as wind, solar, hydroelectric, tidal, wave, geothermal and biofuel. Non-renewable resources will eventually run out: the fossil fuels (coal, oil and natural gas) and nuclear fuel (uranium and plutonium). Burning natural gas also releases carbon dioxide, contributing to global warming, though it emits less CO2 per unit of energy than coal.
GCSE Energy (Physics Paper 1)
Which equation correctly gives the kinetic energy of a moving object?