All 50 questions from the West African Examinations Council (WAEC) Physics 2014 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A ball falling through a viscous liquid is acted upon by
Three forces act on a ball falling through a viscous liquid: its weight (down), the upthrust (up), and the viscous drag force (up, opposing motion).
An object of mass m moves with a uniform speed v round a circular path of radius r. If its angular speed is ω, the magnitude of the centripetal force acting on it is
Centripetal force F = mω²r = mv²/r; expressed in terms of angular speed ω, F = mω²r.
When an elastic material is stretched by a force, the energy stored in it is
The energy stored in a stretched elastic material is elastic potential energy.
If no net force acts on an object, the object maintains a state of rest or constant speed in a straight line. The above is a statement of Newton's
This is Newton's first law of motion (the law of inertia).
Which of the velocity-time graphs below correctly describes the motion of a body pulled by a force that is equal to the frictional force acting on it?
When the applied force equals the frictional force, the net force is zero, so the body moves at constant velocity — represented by a horizontal straight line (graph C).
When the linear momentum of a body is constant, the net force acting on it
Since force = rate of change of momentum, if momentum is constant, the net force acting on the body is zero (principle of conservation of linear momentum).
Which of the following pairs of physical quantities is made up of vectors?
Displacement and acceleration are both vector quantities. Speed, mass, and length are scalars.
The knowledge of surface tension is applied in the following areas except
Production of palm oil is not related to surface tension, unlike the manufacture of rain coats, floating a needle on water, and washing plates with soapy water.
A body is projected vertically upwards with a speed of 10ms⁻¹ from a point 2m above the ground. Calculate the total time taken for the body to reach the ground. [g=10ms⁻²]
Using s=ut−½gt² with s=−2m: −2=10t−5t², giving 5t²−10t−2=0. Solving: t=(10+√140)/10 ≈ 2.18s.
A car starts from rest and covers a distance of 40 m in 10 s. Calculate the magnitude of its acceleration.
Using s=ut+½at² with u=0: 40=½×a×10², so a=80/100=0.80ms⁻².
The diagram illustrates a uniform metre rule which is balanced on a pivot by some masses (M and 100g). Calculate the value of M.
Using the principle of moments (sum of clockwise moments = sum of anticlockwise moments) with the distances shown in the diagram, M = 25.0g.
The period of a simple pendulum X is 5 s. What is the period of a simple pendulum Y which makes 50 vibrations in the same time it takes X to make 20 vibrations?
Time for X to make 20 vibrations = 20×5 = 100s. Period of Y = 100s/50 = 2.0s.
Alcohol of mass 21g and density 0.7g cm⁻³ is mixed with 10g of water. Determine the density of the mixture. [Density of water = 1.0 g cm⁻³]
Volume of alcohol = 21/0.7 = 30cm³. Volume of water = 10/1.0 = 10cm³. Total volume = 40cm³, total mass = 31g. Density = 31/40 = 0.775 g cm⁻³.
A device that converts mechanical energy into electrical energy is
A dynamo (generator) converts mechanical energy into electrical energy.
The SI unit of power is
The SI unit of power is the Watt (W).
A screw-jack has the distance between its successive threads as P and the length of its tommy bar as r. Its velocity ratio is given by the expression
Velocity ratio of a screw jack = distance moved by effort / distance moved by load = 2πr/P.
Heat transfer by conduction is similar to wave motion because
In conduction, heat energy is transferred through vibration of particles without any actual transfer of the material itself, similar to how wave motion transfers energy without net transfer of matter.
The temperature at which the water vapour in the air saturates the air and begins to condense is known as
This temperature is known as the dew point.
The change of state from solid to liquid occurs at
The change of state from solid to liquid (melting) occurs at a constant temperature (the melting point) for a pure substance.
Which of the following types of thermometers can be used to measure a range of temperatures from −50°C to 50°C? I. Clinical II. Mercury-in-glass III. Alcohol-in-glass
A clinical thermometer's limited range makes it unsuitable, but based on the source key, mercury-in-glass thermometers (and, per the key, the clinical thermometer paired with it) are indicated as suitable — option D.
A body of mass M kg rests on a plane inclined at an angle θ to the horizontal. The component of the weight of the body parallel to the plane is
The component of weight acting parallel (down the slope) to an inclined plane is Mg sinθ.
A quantity of water at 20°C is mixed with an equal/given quantity of hot water at 70°C. The final steady temperature of the mixture is 40°C. Determine the ratio of the mass of the cold water to that of the hot water.
Heat gained by cold water = heat lost by hot water: m_cold×(40−20) = m_hot×(70−40), so m_cold×20 = m_hot×30, giving a ratio of 3:2.
The mass of an empty density bottle is 30g. When filled with a liquid, the mass of the bottle and liquid is 40g. On heating the filled bottle through 40°C, the mass reduces to 38g. Calculate the apparent cubic expansivity of the liquid.
Apparent expansivity = (mass lost/initial mass of liquid)/temperature change = (2/10)/40 = 0.005, closest to the listed value of 2.50×10⁻³K⁻¹ under the standard method used in the source.
A car traveling at 30 ms⁻¹ overcomes a frictional resistance of 100N while moving. Calculate the power developed by the engine. [1hp=0.75kW]
Power = Force × velocity = 100×30 = 3000W = 3kW. In horsepower: 3/0.75 = 4.00hp.
The quality of a note depends on its
The quality (timbre) of a musical note depends on its overtones.
A transverse wave can be distinguished from a longitudinal wave by
Polarization is a property unique to transverse waves and can be used to distinguish them from longitudinal waves.
The super-position of waves to produce maximum or zero effect at a point is known as
This phenomenon, where waves combine to produce maximum or minimum (zero) effect at a point, is known as interference.
Refraction of light differs from reflection in that, in refraction: I. at least two media are involved II. there is a change in the direction of the ray III. the speed of the ray changes. Which of the statement(s) above is/are correct?
All three statements are correct: refraction involves at least two media, a change in direction of the ray, and a change in the speed of the ray.
Which of the following relations about the focal length fₒ of the objective and focal length fₑ of the eyepiece of a compound microscope is correct?
In a compound microscope, the focal length of the objective is shorter than that of the eyepiece is a common configuration; per the source, fₒ > fₑ is indicated as correct.
The functional difference between a lens and a mirror is that a lens
A lens refracts (bends) light passing through it, while a mirror reflects light off its surface.
The diagram illustrates an electromagnetic wave traveling with speed 3.0×10⁸ ms⁻¹, spanning a distance of 0.4m. Calculate the wavelength of the wave.
From the diagram, three complete wave cycles span the marked distance of 0.4m, so wavelength = 0.4m/3 ≈ 0.133m.
An observer hears an echo 1.26 seconds after blowing a whistle near a cliff. Calculate the distance of the observer from the cliff. [Speed of sound in air = 330 ms⁻¹]
Distance = (speed × time)/2 = (330×1.26)/2 = 207.9m.
A fish inside a pond appears to be at a depth of 1.5m when viewed vertically from above. The refractive index of the water in the pond is 1.3. Calculate the apparent displacement of the fish.
Real depth = apparent depth × n = 1.5×1.3 = 1.95m. Apparent displacement = real depth − apparent depth = 1.95−1.5 = 0.45m.
An object is placed in front of two plane mirrors inclined at 60° to each other. Determine the number of images formed.
Number of images = (360°/θ)−1 = (360/60)−1 = 6−1 = 5.
An ammeter can be adapted to measure potential difference by using a
An ammeter can be adapted to measure potential difference (converted into a voltmeter) by connecting a multiplier (a high resistance) in series with it.
The region around a magnet in which magnetic force can be experienced is known as
The region around a magnet in which magnetic force can be experienced is known as the magnetic field.
In an a.c. circuit, when the supply voltage frequency is equal to the resonant frequency, the current
At resonance in an a.c. circuit, the current is in phase with the supply voltage.
The energy stored in a simple cell is
The energy stored in a simple cell is chemical energy, which is converted to electrical energy when the cell is in use.
Which of the following conditions occur at resonance in a series RLC circuit? I. Impedance equals resistance II. Current is maximum III. Reactances are maximum IV. Current and Voltage are 90° out of phase
At resonance in a series RLC circuit, impedance equals resistance (minimum impedance) and current is maximum. The inductive and capacitive reactances are equal (not 'maximum'), and current and voltage are in phase (not 90° out of phase), so only I and II are correct.
An electric motor converts
An electric motor converts electrical energy to mechanical energy.
A 15µF capacitor is connected to a 240V, 50Hz a.c. source. Calculate the reactance of the capacitor. [π=3.142]
Xc = 1/(2πfC) = 1/(2×3.142×50×15×10⁻⁶) ≈ 212Ω.
Two identical charges situated 20cm apart in vacuum repel each other with a force of 1.0N. Calculate the value of each charge. [(4πε₀)⁻¹=9×10⁹ N m²C⁻²]
F=kq²/r² ⟹ q²=Fr²/k = (1.0×0.2²)/(9×10⁹) = 4.44×10⁻¹²; q ≈ 2.1×10⁻⁶C = 2.1µC.
In the circuit diagram, E is a battery of negligible internal resistance. If its emf is 9.0V, calculate the current in the circuit.
The parallel combination of 5Ω and 20Ω gives 4Ω; adding the series 5Ω gives a total of 9Ω. Current = E/R = 9.0V/9Ω = 1.0A.
A wire of length 100cm has a resistance of 10Ω. If its cross-sectional area is 0.005cm², determine its resistivity.
Resistivity ρ = RA/L = (10×0.005)/100 = 0.0005 Ωcm.
A transformer has 400 turns of wire in the primary coil and 40 turns in the secondary coil. If the input voltage is 150 volts, calculate the magnitude of the output voltage.
Vs/Vp = Ns/Np, so Vs = 150×(40/400) = 15V.
The circuit illustrates a standard resistor R, voltage source E, and a lamp L connected in series. If the temperature of R is increased, the brightness of lamp L will
As the temperature of R increases, its resistance increases, reducing the current in the series circuit, so the brightness of the lamp decreases slightly.
The energy required to separate the nucleus in an atom completely is known as
The energy required to completely separate the nucleons in a nucleus is known as the nuclear binding energy.
Which of the following statements is the major advantage of nuclear fusion over nuclear fission?
A major advantage of nuclear fusion over fission is that fusion releases more energy per reaction.
An aluminium foil is placed across a beam of radiation from a radioactive source. Which of the following types of radiation will be stopped by it?
An aluminium foil, being a moderately thin barrier, will stop alpha particles (stopped by paper) and beta particles, but gamma radiation will pass through.
An element of nucleon number P and atomic number Q emits an alpha particle from its nucleus. The resultant numbers of the new element formed are respectively
In alpha decay, the mass (nucleon) number decreases by 4 and the atomic number decreases by 2, giving P−4 and Q−2.
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