Physics and Applied Mechanics
What this domain tests
Physics and Applied Mechanics tests the physical principles behind tools, machines, and structures: units, motion, forces, moments, work, energy, power, pressure, and simple equilibrium. Questions often use a practical setup rather than a pure formula.
Core rules
- Use SI units: metre, kilogram, second, newton, joule, watt, pascal. Weight W = mg, with g ≈ 9.81 m/s².
- For constant acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.
- Resultant force changes motion; equilibrium means net force and net moment are zero.
- Moment = force × perpendicular distance from the pivot. Work = force × distance moved in the force direction. Power = work ÷ time.
- Mechanical advantage = load ÷ effort; efficiency = useful output ÷ input × 100%.
Worked example
A 12 kg crate is lifted vertically 3.0 m in 4.0 s at steady speed. Find the work done and the average power. Weight = 12 × 9.81 = 117.7 N. Work = 117.7 × 3.0 = 353 J. Power = 353 ÷ 4.0 = 88.3 W. At steady speed the lifting force equals the weight; if the crate were accelerated, an extra net force would be needed.
Traps
- Reporting mass in newtons or weight in kilograms.
- Using the sloped distance as the moment arm instead of the perpendicular distance.
- Forgetting that work requires movement in the direction of the force.
- Mixing watts, kilowatts, and joules without converting.