MINDMAPS FOR UPSCPET 2026 · VISUAL REVISION
Work, power, energy and machine advantage
Calculate mechanical advantage and convert commercial electrical units to joules
Machines, power and energy units
Mechanical advantage (MA)
- Mechanical advantage MA = Load (L) ÷ Effort (E); it has no unit as newtons cancel.
- Worked example: lifting a 200 N load with a 50 N effort gives MA = 200 ÷ 50 = 4.
- MA > 1 means the machine multiplies force; MA < 1 trades force for speed or range.
Work and conservation of energy
- Work W = F × d cos θ; SI unit is the joule (1 J = 1 N × 1 m).
- In an unpowered machine with no stored-energy release, output work cannot exceed input work.
- For an ideal machine, a fourfold force gain needs fourfold effort distance.
Power: rate of doing work
- Power P = Work ÷ time = Energy ÷ time; SI unit is the watt (1 W = 1 J s⁻¹).
- 1 kilowatt = 1000 watts = 1000 joules per second.
- Do not confuse power (rate of use) with energy (power × time).
Kilowatt-hour (kWh) to joules
- 1 kWh is the energy used by a 1 kW device running for 1 hour (3600 seconds).
- Conversion: 1 kWh = 1000 W × 3600 s = 3,600,000 J = 3.6 × 10⁶ J.
- Electricity consumption is commonly billed in units of 1 kWh.
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