External Assessment Paper 2: Extended Response and Problem Solving
Paper 2 asks you to build multi-step solutions and justify reasoning. Expect combined problems: a projectile followed by an energy calculation, a charged particle moving through both electric and magnetic fields, or a circuit analysed with Kirchhoff's rules. Marks are allocated to method, so show the equation, the substitution with units, and the answer with direction where relevant.
Concepts to command
- Projectile motion: horizontal and vertical components are independent; horizontal velocity is constant, vertical acceleration is g.
- Circular motion: centripetal force is the net inward force, not an extra force to add to a free-body diagram.
- Fields: field strength is force per unit charge or per unit mass; potential is energy per unit charge or mass.
- Induction: a changing flux linkage produces an emf; Lenz's law gives the direction opposing the change.
- Quantum: photon energy equals hf, and photoelectric emission requires energy above the work function.
Traps to watch
- Adding centripetal force alongside tension or gravity instead of recognising it as the resultant.
- Confusing electric potential energy with electric potential.
- Using total velocity in one component equation.
- Forgetting that an induced current opposes the change in flux, not the flux itself.
Worked example
A 2.0 kg mass on a string of length 1.5 m swings at the top of a vertical circle at 4.0 m/s. Find the tension. At the top, gravity and tension both point down toward the centre: T + mg = mv^2/r. So T = (2.0 x 16)/1.5 - (2.0 x 9.8) = 21.3 - 19.6 = 1.7 N. If you had added a separate centripetal force you would double-count.
Rule of thumb
Write the net-force equation toward the centre first, then substitute. Always ask whether a force is the resultant or a contributor.