General Engineering and Applied Sciences: Units, Physics, and Economics
Coverage of this domain
This section samples broadly: mechanics (kinematics, Newton's laws, work-energy, momentum), fluid mechanics, thermodynamics (ideal gas law, first law, heat engines, entropy), basic chemistry (moles, stoichiometry, pH, oxidation-reduction), materials (stress, strain, Young's modulus, elastic limit), and engineering economy (simple and compound interest, effective rate, depreciation, break-even, present worth). Engineering ethics, safety, and contracts occasionally appear as short conceptual items.
Traps that recur
- Gauge versus absolute pressure: P_abs = P_gauge + P_atm. Gauges read zero at atmospheric pressure.
- Temperature in the ideal gas law must be in kelvin, never Celsius.
- Mass versus weight; the newton versus the kilogram-force.
- Stress is force divided by area - an item that gives force alone is a distractor.
- Nominal versus effective annual interest rate; effective rate compounds.
- Straight-line depreciation spreads the depreciable base (cost minus salvage), not the full cost.
Worked example
A machine costs P100,000 with a salvage value of P10,000 after 9 years. Straight-line annual depreciation = (cost − salvage)/life = (100,000 − 10,000)/9 = P10,000 per year. Book value after 4 years = 100,000 − 4(10,000) = P60,000.
Rule of thumb
Carry units through every step and cancel them as if they were algebraic symbols; a mismatched unit flags the wrong formula before any arithmetic is done. For economy problems, sketch a cash-flow arrow diagram - it separates present from future amounts and prevents exponent slips.
Keep significant figures consistent with the given data, and convert all prefixes to base units at the start.