Topic 3 of 8 · Form 3
Energy, work, power and pressure
Kinetic, gravitational potential, chemical, elastic, internal (thermal), nuclear and electrostatic stores; energy is transferred mechanically, electrically, by heating and by radiation. Conservation of energy.
Notes for this topic 1 file, in order
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Energy stores and transfers
Kinetic, gravitational potential, chemical, elastic, internal (thermal), nuclear and electrostatic stores; energy is transferred mechanically, electrically, by heating and by radiation. Conservation of energy.
- Ek = ½mv²; ΔEp = mgΔh.
- Work done = force × distance moved in the direction of the force.
- Power = work done ÷ time = energy transferred ÷ time.
- Efficiency = useful energy output ÷ total energy input × 100%.
Worked example: A 0.5 kg ball is dropped from 5 m. Find its speed just before impact (g = 9.8 m/s²).
mgh = ½mv² → v = √(2 × 9.8 × 5) = 9.9 m/s
Energy resources
Fossil fuels, nuclear, hydroelectric (Kariba), solar, wind, geothermal, tidal and biofuels – advantages and disadvantages (renewable or not, reliability, cost, pollution).
Pressure
p = F/A; pressure in liquids Δp = ρgΔh.
Worked example: Find the pressure due to water at a depth of 8 m (ρ = 1 000 kg/m³, g = 9.8).
p = 1 000 × 9.8 × 8 = 78 400 Pa
Check yourself
- A motor does 4 500 J of work in 15 s. Find its power.
- Why is solar energy described as renewable?
- A force of 600 N acts on 0.03 m². Find the pressure.
Show answers
- 300 W
- It will not run out on a human timescale.
- 20 000 Pa
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