Physics - mechanics and energy
What the exam tests
Fukui mechanics questions ask you to read motion from graphs, balance forces, and apply work–energy reasoning in everyday contexts. You should switch confidently between force, acceleration, velocity and energy.
Core rules
- Newton's first law: zero net force means constant velocity, including rest.
- Newton's second law: F = ma. Weight is mg, not mass.
- Work: W = Fd cos θ, in joules. Only the component along displacement does work.
- Kinetic energy: Ek = ½mv². Gravitational potential energy: Ep = mgh.
- Conservation of energy: energy is transferred, not destroyed; friction converts mechanical energy to heat.
- Efficiency = useful output energy ÷ input energy × 100%.
Worked example
A 2.0 kg box starts from rest and is pushed 5.0 m across a frictionless floor by a horizontal 10 N force. Work = 10 × 5.0 = 50 J. This becomes kinetic energy: 50 = ½ × 2.0 × v², so v² = 50 and v ≈ 7.1 m/s. If 10 J were lost to friction, only 40 J would remain, giving v² = 40 and v ≈ 6.3 m/s.
Traps
- A force perpendicular to motion, such as a normal force on a horizontal floor, does no work.
- Do not use weight in newtons where mass in kilograms is required in ½mv².
- On a velocity–time graph, area is displacement and gradient is acceleration; on a distance–time graph, gradient is speed.