Mechanics, Motion and Energy
Dynamics covers motion (kinematics) and its causes (kinetics). Candidates must use equations of motion for constant acceleration: v = u + at; s = ut + ½at²; v² = u² + 2as. Understand Newton's laws, friction (F = μN), and circular motion (centripetal acceleration a = v²/r).
Energy concepts: kinetic energy (½mv²), gravitational potential energy (mgh), work (W = F·s·cosθ), power (P = W/t = Fv), and conservation of energy (with losses to friction/heat). Distinguish momentum (p = mv) and its conservation in collisions (elastic vs inelastic). Understand efficiency = useful output / total input × 100%.
Traps
Mixing units (km/h to m/s: divide by 3.6). Assuming constant acceleration when it is not. Forgetting that friction does negative work. In collisions, kinetic energy is conserved only in elastic collisions; momentum is conserved in both. Watch for energy 'lost' being converted, not destroyed. Circular motion: centripetal force points to centre, not outward (centrifugal is a pseudo-force).
Worked rule of thumb
For a falling object from rest through height h: v = √(2gh). Example: h = 5 m, g = 9.81 → v ≈ 9.9 m/s. Alternatively use energy: mgh = ½mv², mass cancels. Always check direction of acceleration and sign conventions.