Physics
Core concepts
You must be able to handle SI base and derived units and their prefixes; scalars versus vectors; linear motion (velocity, acceleration, equations of uniformly accelerated motion); Newton's three laws; moments, couples and equilibrium; work, energy, power and efficiency; and momentum. Matter and fluids covers density, specific gravity, pressure (hydrostatic and pneumatic), Pascal's law, buoyancy, and the gas laws. Thermodynamics covers heat, temperature scales, specific heat, latent heat, and the three modes of heat transfer: conduction, convection and radiation. Also expect simple harmonic motion, waves, the speed of sound, and the basics of light and optics.
Traps in questions
- Mass versus weight. Mass is kilograms and does not change with location; weight is force in newtons and does.
- Gauge versus absolute pressure. Absolute = gauge + atmospheric. Gas law calculations need absolute.
- Temperature in kelvin for gas-law and efficiency problems.
- Units of moments are N·m, not N/m.
- Efficiency is always less than 1; if your answer exceeds it, you inverted the ratio.
Worked example
A hydraulic piston has an area of 0.01 m² and sees a pressure of 2 MPa. Force = pressure × area = 2 × 10⁶ × 0.01 = 20 000 N, i.e. 20 kN. If that force acts through a stroke of 0.05 m, work done = F × d = 20 000 × 0.05 = 1000 J, and if it takes 0.5 s, power = 1000/0.5 = 2000 W = 2 kW.
Rule of thumb
Standard atmosphere at sea level: 1013.25 hPa, 15 °C, density 1.225 kg/m³. Speed of sound in dry air ≈ 331 + 0.6 × T(°C) m/s.