Physics: Forces and Motion, Energy, Electricity and Magnetism, Waves and Sound
Forces and motion
The exam tests whether you can connect forces to motion and read motion graphs. An object stays at rest or in uniform motion unless a net force acts. Acceleration is proportional to net force and inversely proportional to mass (F = ma). Every action has an equal and opposite reaction, but the two forces act on different bodies. On a displacement–time graph the slope is velocity; on a velocity–time graph the slope is acceleration and the area underneath is displacement. For uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as.
Energy
Work = force × distance moved in the direction of the force. Kinetic energy = ½mv² and gravitational potential energy = mgh. In a closed system total energy is conserved; friction transfers mechanical energy to heat and sound.
Electricity and magnetism
Ohm's law: V = IR. In series, R = R₁ + R₂ and current is the same everywhere. In parallel, 1/R = 1/R₁ + 1/R₂ and voltage is the same across each branch. Power P = VI = I²R. A current creates a magnetic field; a changing magnetic field induces a voltage, which is how generators work.
Waves and sound
Wave speed v = fλ. Sound is longitudinal, needs a medium, and travels about 340 m/s in air, faster in solids. Pitch depends on frequency, loudness on amplitude. Reflection, refraction and diffraction apply to all waves.
Worked example
A 2 kg cart starts from rest and accelerates at 3 m/s² for 4 s. v = 0 + 3×4 = 12 m/s. s = ½×3×4² = 24 m. Kinetic energy = ½×2×12² = 144 J.
Traps
Do not cancel action–reaction pairs; they act on different objects. Weight in newtons is not mass in kilograms. Check whether a graph question asks for slope or area. In parallel circuits the smallest resistor carries the largest current. Sound cannot cross a vacuum, and doubling amplitude does not raise pitch.