WAEC Physics 2019
Questions & Answers

Acceleration is defined as the rate of change of velocity with respect to time. It measures how quickly an object changes its speed or direction.

Momentum is a vector quantity because it has both magnitude (mass times speed) and direction (same as velocity). Volume, energy, and speed are scalar quantities with magnitude only.

In an elastic collision, both linear momentum and kinetic energy are conserved. This differs from inelastic collisions where only momentum is conserved, and kinetic energy is not.

Lenz's law states that the direction of the induced current is such that it opposes the change in magnetic flux that produces it, based on the conservation of energy.

A gold leaf electroscope can detect and compare charges by observing the deflection of the gold leaf, which is proportional to the charge magnitude when charges are shared sequentially.

Initial potential energy = mgh = 2 × 10 × 100 = 2000 J. After falling 80 m, potential energy left = 2 × 10 × 20 = 400 J. Thus, kinetic energy = 2000 - 400 = 1600 J.

Radio waves are electromagnetic waves that do not require a medium for propagation, unlike mechanical waves such as sound, water, and waves in pipes, which need a material medium.

The restoring force in a spring undergoing simple harmonic motion is the elastic force provided by the spring, following Hooke's law: F = -kx, where x is displacement from equilibrium.

Total internal reflection occurs only when light travels from a denser to a rarer medium at an angle greater than the critical angle. From air (rarer) to water (denser), refraction occurs, not TIR.

A vacuum prevents conduction and convection as there is no medium for heat transfer by these modes. Radiation is minimized separately by reflective surfaces.

Acceleration a = (final velocity - initial velocity) / time = (20 - 0) / 5 = 4 m/s². Wait, that's B. Wait, 20/5=4, yes B. Wait, options A 2 B4. Correct B.

According to Newton's first law, an object moving at constant velocity has zero net force acting on it, as there is no acceleration.

From Newton's second law, F = ma. If acceleration a = 0, then net force F = 0.

Placing a demagnetized bar magnet east-west aligns it perpendicular to the Earth's magnetic field (north-south), minimizing realignment of domains and helping retain demagnetization.

Ohm's law: V = IR, so R = V/I = 12/2 = 6 Ω.

Introducing air increases the pressure above the mercury column, which pushes down on the mercury, lowering the level in the tube as atmospheric pressure now supports less height.

Heat to melt ice: Q1 = m L_f = 0.06 × 3.36 × 10^5 = 20,160 J. Heat to raise water temp: Q2 = m c ΔT = 0.06 × 4200 × 80 = 20,160 J. Total Q = 40,320 J = 40.32 kJ.

Using R_t = R_0 (1 + α t), α = (10.5 - 3.5)/(3.5 × 100) = 0.02 K⁻¹. Then t = (7.5 - 3.5)/(3.5 × 0.02) = 4 / 0.07 ≈ 57°C.

Speed v = distance / time = 4.5 / 0.6 = 7.5 m/s. Wavelength λ = v / f = 7.5 / 9 ≈ 0.83 m.

Sound speed is lowest in air (≈ 340 m/s) compared to solids like brass (≈ 5000 m/s) and wood (≈ 4000 m/s), and liquid water (≈ 1500 m/s), due to air's lower density and elasticity.

A ripple tank demonstrates wave reflection (off barriers), refraction (through varying depth regions), and diffraction (around obstacles or through slits) effectively for water waves.

Conservation of momentum: (800 × 80 + 1200 × 40) = (800 + 1200) v → (64,000 + 48,000) = 2000 v → v = 112,000 / 2000 = 56 km hr⁻¹.

From F = ma, a = F/m. New a' = (F/2) / (2m) = F/(4m) = a/4, so quartered.

A maximum-minimum thermometer (Six's) records the highest temperature reached during the day and the lowest at night since the last reset, using alcohol and mercury indicators.

Replacing slip rings (for AC output) with a commutator reverses the current direction every half rotation, producing pulsating DC output in a generator.

Soft iron has low retentivity, losing magnetism quickly when the current stops, allowing the armature to retract rapidly for continuous bell ringing.

The joule (J) is the SI unit of energy, defined as the work done by a force of 1 N over 1 m. Newton is force, watt is power, pascal is pressure.

For free fall, v = u + gt = 0 + 10 × 3 = 30 m/s.

Frequency f = 1 / period T = 1 / 2 = 0.5 Hz.

Boyle's law states that for a fixed mass of gas at constant temperature, pressure P is inversely proportional to volume V: P ∝ 1/V.

The coulomb (C) is the SI unit of electric charge, equivalent to the charge transported by 1 ampere in 1 second.

Wavelength λ = speed / frequency = 340 / 850 = 0.4 m.

Copper is a metal with free electrons, allowing easy flow of electric current, unlike insulators like rubber, glass, and wood.

Efficiency = (output / input) × 100%, so 80 = (400 / input) × 100 → input = 400 / 0.8 = 500 J.

Kinetic energy KE = (1/2) m v² = 0.5 × 5 × 9 = 22.5 J.

Resultant R = √(10² + 20²) = √(100 + 400) = √500 ≈ 22.4 N (Pythagoras theorem for perpendicular forces).

Heat Q = m c ΔT = 2 × 400 × 10 = 8000 J.

Distance is a scalar quantity with magnitude only, while velocity, acceleration, and force are vectors with both magnitude and direction.

Power P = I² R = 5² × 10 = 25 × 10 = 250 W.

The law of reflection states that the angle of incidence equals the angle of reflection, and the incident ray, reflected ray, and normal lie in the same plane.