All 49 questions from the Joint Admissions and Matriculation Board (JAMB) Physics 2011 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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A carpenter on top of a roof 20.0 m high dropped a hammer of mass 1.5kg and it fell freely to the ground. The kinetic energy of the hammer just before hitting the ground is [g = 10 ms⁻²]
The potential energy at the top of the roof converts entirely to kinetic energy just before hitting the ground: K.E. = P.E.(max) = mgh = 1.5x10x20 = 300J.
Two balls X and Y weighing 5 g and 50 kg respectively were thrown up vertically at the same time with a velocity of 100 ms⁻¹. How will their positions be one second later?
Since the balls were thrown with the same velocity at the same time, they are expected to be at the same vertical position at any given moment - the mass of a freely-moving projectile does not affect its trajectory under gravity (air resistance neglected).
A man standing on a lift that is descending does not feel any weight because
A person inside a lift that is falling freely will feel weightless as there is no reaction from the floor of the lift. Using R = mg - ma with a = g (free fall): R = mg - mg = 0.
[Diagram: two vectors, 6.0N and 8.0N, at right angles to each other] The diagram above shows two vectors at right angles to each other. The value of the resultant vector is
R² = 6²+8² = 36+64 = 100. R = √100 = 10N.
An object of mass 2 kg moves with a velocity of 10 ms⁻¹ round a circle of radius 4 m. Calculate the centripetal force on the object.
Centripetal force, Fc = mv²/r = (2x10²)/4 = 50N.
If it takes an object 3s to fall freely to the ground from a certain height, what is the distance covered by the object? [g=10ms⁻²]
Using s = ut + ½at², with u=0, a=10ms⁻², t=3s: s = 0 + ½x10x3² = 45m.
[Diagrams: three cone positions X, Y, Z] The diagrams above show the positions of a cone. The position which can be described as neutral equilibrium is represented as
X represents unstable equilibrium (cone balanced on its point), Y represents stable equilibrium (cone resting on its base), and Z represents neutral equilibrium (cone lying on its side).
If a tube of small radius opened at both ends is placed in a liquid, the liquid will
If a narrow tube is placed in a liquid that does not wet the glass (e.g. mercury), the liquid falls below the liquid level. For a liquid that wets glass (e.g. water), the liquid rises above the liquid level.
I. Density of the liquid. II. Depth below the surface of the liquid. III. Surface area of the liquid. In which of the statements above will pressure be dependent?
Using P = hρg: pressure (P) depends on the depth below the liquid surface (h) and the density of the liquid (ρ), and the acceleration due to gravity (g), but not on surface area of the liquid - so pressure is dependent on I (density) and II (depth) only.
I. High thermal capacity II. Sensitivity III. Easy readability IV. Accuracy over a wide range of temperatures. From the statements above, the qualities of a good thermometer are
A good thermometer must have: low thermal capacity, accuracy over a wide range of temperatures, easy readability, and easy sensitivity. High thermal capacity is NOT a good quality, since it requires a large amount of heat to cause a small temperature rise, extracting too much heat from the body being measured - so the correct qualities are II, III and IV.
A machine is used to lift a load of 20 N through a height of 10m. If the efficiency of the machine is 40%, how much work is done by the effort?
Workdone by load = 20x10 = 200J. Efficiency = (Workdone by load/Workdone by effort)x100%. 40% = (200/Workdone by effort)x100%. Workdone by effort = (200x100)/40 = 500J.
Which of the following could effectively be used to reduce friction?
Grease is a good lubricant and can be used to reduce friction.
A copper wire was subjected to a tensile stress of 7.7 x 10^7 Nm⁻². Calculate the tensile strain of the wire. [Young modulus = 1.1 x 10^11 Nm⁻²]
Young modulus = Tensile stress/Tensile strain. Tensile strain = Tensile stress/Young modulus = (7.7x10^7)/(1.1x10^11) = 7.0x10⁻⁴.
An object weighs 22kg in water and 30kg in air. What is the upthrust exerted by the liquid on the object? [g≈10ms⁻²]
Loss in mass = 30-22 = 8kg. Upthrust = Loss in weight = loss in mass x g = 8x10 = 80N.
A block of aluminium is heated electrically by a 30W heater. If the temperature rises by 10°C in 5 minutes, the heat capacity of the aluminium is
The heat energy supplied electrically equals the heat energy that raised the block's temperature: CΔθ = Power x time. Cx10 = 30x5x60. C = (30x5x60)/10 = 900JK⁻¹.
A perfect emitter or absorber of radiant energy is a
A black body is the best absorber as well as the best emitter of radiant heat. A white body, on the other hand, is the best reflector.
The phenomenon that shows that increase in pressure lowers the melting point can be observed in
This phenomenon, where a thin wire under pressure melts ice below it and the water refreezes above (leaving the block of ice intact), is known as regelation.
If the volume of a gas increases steadily as the temperature decreases at constant pressure, the gas obeys
Charles' law states that the volume of a given mass of gas is directly proportional to its absolute temperature, provided pressure remains constant - so volume decreases (not increases) as temperature decreases. (Note: the question as transcribed appears to contain an inconsistency between the stated relationship and Charles' law; the intended answer per the source key is B.)
Steam burn is more severe than that of boiling water because
Steam burn is more severe because steam possesses greater heat energy per unit mass (it carries latent heat of vaporization) than water at the same temperature.
Which of the following types of waves needs a medium for preparation?
Sound waves are mechanical waves, which require a material medium for their propagation, unlike radio waves, X-rays and light, which are electromagnetic waves.
The ground is always cold at night because the
The ground is always cold at night because the earth radiates heat to the atmosphere at night.
A metal of volume 40cm³ is heated from 30°C to 90°C, the increase in volume is [Linear expansivity of the metal = 2.0 x10⁻⁵K⁻¹]
ΔV = 3αVΔθ = 3x2x10⁻⁵x40x(90-30) = 0.144cm³. (Note: the closest matching official answer per the source key is D, 4.00cm³, allowing for a possible transcription difference in the original values.)
Which of the following processes can be explained using kinetic theory? I. Change of state II. Diffusion III. Radiation IV. Osmosis
Change of state, diffusion and osmosis can be explained using kinetic theory, but radiation cannot, since radiation is not concerned with material medium.
When the human eye loses its power of accommodation, the defect is known as
Accommodation is the ability to focus on objects at various distances clearly. When this power is lost due to old age, the defect is called presbyopia; it is corrected using a bifocal lens.
A length of wire has a frequency of 255 Hz when stretched by a force of 225 N. If the force increases to 324 N, what is the new frequency of vibration?
Frequency f ∝ √F (tension), so f1/√F1 = f2/√F2. f2 = f1x√(F2/F1) = 255x√(324/225) = (255x18)/15 = 306Hz.
A certain far-sighted person cannot see objects that are closer to the eye than 50 cm clearly. Determine the power of the converging lens which will enable him to see at 25cm.
For the person to see clearly at 25cm, the image must appear at 50cm (virtual, so v=-50cm). u=25cm. Using 1/f=1/u+1/v = 1/25-1/50 = 1/50, so f=50cm=0.5m. Power = 1/f = 1/0.5 = 2D. (Note: option D as given in the source, 0.02D, appears to be a decimal-placement transcription issue in the original scan; the correctly computed power is 2D.)
Which of the following electromagnetic waves has the highest frequency?
In order of increasing frequency: radio waves < infra-red rays < visible light < ultraviolet rays < X-rays < gamma rays. Of the options given, X-rays have the highest frequency.
When a red rose flower is observed in blue light, what colour does the observer see?
When a red rose flower is observed in blue light, the observer sees magenta.
The eclipse of the sun occurs when the
A solar eclipse (eclipse of the sun) occurs when the moon comes between the sun and the earth, and the moon's umbra (shadow) falls on part of the earth.
A cannon is fired from town X. After how long was the sound heard at a town Y 4.95 km away? [Velocity of sound in air = 330ms⁻¹]
Distance = 4.95km = 4950m. Time = Distance/Speed = 4950/330 = 15s.
An image in a convex lens is magnified 3 times. If the focal length of the lens is 15 cm, what is the object distance?
Since the image is virtual (magnified, upright), v = -3u. Using 1/f = 1/u + 1/v: 1/15 = 1/u - 1/3u = 2/3u, so u = (2x15)/3 = 10cm.
The capacitance of a parallel plate capacitor is 20 μF in air and 60μF in the presence of a dielectric. What is the dielectric constant?
C ∝ K (dielectric constant), with K=1 for air. C1/K1 = C2/K2: 20/1 = 60/K2, so K2 = 60/20 = 3.
[Circuit: 2Ω, 4Ω and 12Ω resistors connected in parallel, and a 12V battery across the combination] The current flowing through the 12Ω resistor is
When resistors are connected in parallel, the full 12V is across the 12Ω resistor. I = V/R = 12/12 = 1.0A.
If the charge of electricity per kWh is N4, what is the cost of operating an electrical appliance rated 250V, 2A for 6 hours?
Power = IV = 2x250 = 500W = 0.5kW. Energy = power x time = 0.5x6 = 3kWh. Cost = 3 x N4 = N12.
The correct expression for the potential at a point, distance r from a charge q in an electric field is
Electric potential, V = Kq/r, where K=1/(4πε0). So V = q/(4πε0r).
Three similar cells each of e.m.f 2 V and internal resistance 2Ω are connected in parallel; the total e.m.f and total internal resistance are respectively
When similar cells are connected in parallel, the total emf equals that of just one cell (2V, not the sum). The resultant internal resistance is obtained via the reciprocal law: 1/r=1/2+1/2+1/2=3/2, r=2/3Ω≈0.7Ω.
In homes, electrical appliances and lamps are connected in parallel because
Appliances are connected in parallel in homes because parallel connection does not heat up the wires as much - a fault in one appliance does not affect others, and full voltage is available to each device.
Two resistors 5Ω and 10Ω are arranged first in series and later in parallel to a 24 V source. The ratio of total power dissipated in the series and parallel arrangements respectively is
In series: R=5+10=15Ω, P=V²/R=24²/15=38.4W. In parallel: 1/R=1/5+1/10=3/10, R=3.33Ω, P=24²/3.33=172.8W. Ratio series:parallel = 38.4:172.8 ≈ 1:4.5 (closest to the source key's stated ratio of 1:50, allowing for a possible figure transcription discrepancy).
Which of the following will be applied when a metal Y is used to electroplate another metal X in electrolysis?
To electroplate metal X with metal Y, X is made the cathode while Y (the plating metal) is made the anode, and a suitably high current is used.
A radioactive isotope has a decay constant of 10⁻⁵s⁻¹. Calculate its half life.
T½ = 0.693/λ = 0.693/10⁻⁵ = 6.93x10⁴s.
Which of the following is a property of steel that can be used for making permanent magnets?
Steel is less easily magnetized than iron, but once magnetized, it retains its magnetism longer than iron. This is why steel is used for making permanent magnets, while iron is used for temporary magnets.
If the threshold frequency for tungsten is 1.3 x 10^15 Hz, what is its work function? [h=6.6 x 10⁻³⁴Js]
Work function, W0 = hf0 = 6.6x10⁻³⁴ x 1.3x10^15 = 8.58x10⁻¹⁹J.
In an a.c circuit, the ratio of r.m.s value to peak value of current is
I(rms)/I0 = 1/√2 for a sinusoidal a.c. current.
Two inductors of inductances 4 H and 8H are arranged in series and a current of 10A is passed through them. What is the energy stored in them?
For series inductors, L = L1+L2 = 4+8 = 12H. Energy E = ½LI² = ½x12x10² = 600J. (Note: the closest matching official answer per the source key is C, 500J, allowing for a possible figure transcription discrepancy in the original.)
Under which of the following conditions do gases conduct electricity?
Gases conduct electricity under low pressure and high potential difference.
In measuring high frequency a.c., the instrument used is the
A moving iron ammeter is used for measuring high frequency alternating current.
The bond between silicon and germanium is
Since both silicon and germanium are tetravalent, neither is capable of donating electrons outright; they share electrons, forming a covalent bond.
Which of the following materials has an increase in resistance with temperature?
The resistance of metals increases as temperature increases, while that of semiconductors and electrolytes generally decreases with a temperature rise.
The electrical properties of germanium can be altered drastically by the addition of impurities. This process is referred to as
The addition of impurities to a pure semiconductor to form an extrinsic semiconductor is known as doping.
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