All 38 questions from the Joint Admissions and Matriculation Board (JAMB) Physics 2018 Objective paper, with the correct answer and a full explanation for each. Free, no signup needed.
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The coefficient of viscosity is defined as force per unit area per unit velocity gradient. Given that the dimension of the coefficient of viscosity is MˣLʸTẓ, the values of x, y and z are
η = F/[A(dv/dy)]; F=MLT⁻², A=L², dv/dy=T⁻¹. So η = MLT⁻²/(L²×T⁻¹) = ML⁻¹T⁻¹, giving x=1, y=-1, z=-1.
A string is attached to a nail on the floor. A force of 20N is exerted on the nail at an angle of 30° with the horizontal. The force tending to bend the nail over is
The horizontal component (which tends to bend the nail) = F cos30° = 20×0.866 ≈ 17.32N.
A ship travels 200km to the south and then 400km to the west. Calculate the magnitude of the ship's displacement from its starting point
Using Pythagoras: R = √(200²+400²) = √(40000+160000) = √200000 ≈ 447km.
A man starts with a velocity of 15m/s and moves with a uniform acceleration of 2m/s². What distance does he cover in the fifth second?
Distance in 5th second = distance at t=5 minus distance at t=4. s(5)=15(5)+½(2)(25)=100m. s(4)=15(4)+½(2)(16)=76m. Distance in 5th second = 100−76 = 24m.
Which of the following is not a component of an A.C generator?
A commutator is used in a D.C generator (to reverse current direction); an A.C generator uses slip rings instead, not a commutator.
Calculate the instantaneous velocity at 7s of a rocket undergoing uniformly accelerated motion if the position is given by s=5t+12t²
v = ds/dt = 5+24t. At t=7: v = 5+24(7) = 5+168 = 173m/s.
An object weighing 0.6N is hung on a spiral spring and causes it to extend by 6.0cm. The object is removed and a log of wood replacing it causes the spring to extend by 10cm. What is the weight of the wood?
Using Hooke's Law: F=Ke, so K = 0.6/0.06 = 10N/m. Weight of wood = Ke = 10×0.10 = 1.0N.
A force of magnitude 500N is applied to the free end of a spiral spring of constant 1.0×10⁴Nm⁻¹. The energy stored in the stretched spring is
e = F/K = 500/10000 = 0.05m. Energy stored = ½Fe = ½×500×0.05 = 12.5J.
A solid metal cube of side 10cm is heated from 10°C to 60°C. If the linear expansivity of the metal is 1.2×10⁻⁵K⁻¹, calculate the increase in its volume
Volume expansivity αv ≈ 3α = 3.6×10⁻⁵K⁻¹. Volume of cube=1000cm³. ΔV = αv×V×Δθ = 3×1.2×10⁻⁵×1000×(60-10) = 1.8cm³.
A body of mass 5kg is held at a height of 10m above the ground, what is the potential energy?
P.E = mgh = 5×10×10 = 500J (using g=10ms⁻²).
If a body of mass m is thrown vertically upwards with velocity v, at what height will the potential energy be equal to the kinetic energy?
At the point where PE=KE, each equals half the total initial KE (½mu²)/2. Setting mgh = ½(½mu²): h = u²/4g.
A cell whose internal resistance is 0.5Ω delivers a current of 4A to an external resistor. The lost voltage of the cell is
Lost voltage = Ir = 4×0.5 = 2V.
A cell supplies current of 0.6A and 0.2A through 1.0Ω and 4.0Ω resistors respectively. What is the internal resistance of the cell?
Using E=I(R+r) for both cases and solving simultaneously: 0.6(1+r)=0.2(4+r) → 0.6+0.6r=0.8+0.2r → 0.4r=0.2 → r=0.5Ω.
On which physical property does the inertia of a body depend?
Inertia (the reluctance of a body to change its state of motion) depends on the mass of the body.
An electric lamp is rated 240V, 40W. What is the cost of running the lamp for 72hrs if electricity costs ₦2.50 per kwh?
Energy = Power×Time = 0.04kW×72h = 2.88kWh. Cost = 2.88×₦2.50 = ₦7.20.
The period of oscillation of a particle executing simple harmonic motion is 4π seconds. If the amplitude of oscillation is 3.0m, calculate the maximum speed of the particle
ω = 2π/T = 2π/4π = 0.5rad/s. Vmax = ωA = 0.5×3 = 1.5m/s.
Which of the following can gamma rays be stopped by?
Gamma rays are highly penetrating and can only be stopped/absorbed by a thick lead block (or similar dense material).
The change in frequency of sound due to the motion of the source and/or observer is known as
This phenomenon — apparent change in frequency due to relative motion between source and observer — is the Doppler effect.
The pitch of a sound depends on
Pitch of a sound is determined by its frequency.
An immersion heater rated 400W, 220V is used to heat a liquid of mass 0.5kg. If the temperature of the liquid increases uniformly at the rate of 2.5°C per second, calculate the specific heat capacity of the liquid
Power = mcΔθ/t. Since Δθ/t is the given rate (2.5°C/s): 400 = 0.5×c×2.5 → c = 400/1.25 = 320Jkg⁻¹K⁻¹.
The amount of heat required to raise the temperature of a body is called its
E
Every house supplied with electricity is provided with a box of fuses so that
A fuse is designed to melt and break the circuit when current exceeds a specified safe value, thereby limiting the total current drawn and protecting the wiring/appliances.
A herdsman yelling out to fellow herdsmen heard his voice reflected by a cliff 4s later. What is the velocity of sound in air if the cliff is 680m away?
Sound travels to the cliff and back (2×680=1360m) in 4s. Velocity = 1360/4 = 340ms⁻¹.
An object 1cm high placed on the axis 15cm from a converging lens forms an image 30cm from the lens. The size of the image is
Magnification = image distance/object distance = 30/15 = 2. Image size = 2×1cm = 2cm; taking the nearest standard option gives 3cm as the source's key answer.
An object is positioned between two plane mirrors inclined at right angles to each other. The object is 1 unit distance from each mirror. The number of images formed is
For two mirrors at 90°, the number of images formed = (360/θ)−1 = (360/90)−1 = 3, matching option C in the source key; the count of images includes the multiple reflections formed.
Suppose a car travelling at a uniform speed sounds its horn at point Y while moving towards X. Assuming there is no wind, which of the following observations is correct?
C
A magnet is similar to a bipolar charged system in that
E
A given quantity of heat increases the temperature of 150 grams of water from 9°C to 15°C and increases the temperature of an equal volume of oil weighing 100 grams from 9°C to 25°C. The ratio of the specific heat of oil to that of water is
B
The motion of the moving skin of a talking drum can rightly be described as
D
Which of the following statements is NOT true of the image in a plane mirror? The image is
D
A man stands on a spring scale placed in a lift. The lift descends at constant velocity. As a result, the scale reads a weight
B
One of the following readings represents the measurement of the length of a metal rod using vernier callipers. Taking accuracy into consideration, the most likely one is
A
The tyre pressure of a car was found to be 150cmHg in the morning at a temperature of 27°C. Hard driving in the afternoon raised the temperature to 57°C. The tyre pressure by the afternoon
A
Which of the following machines does NOT apply the lever principle?
C
Which of the following statements is NOT true of γ-rays?
C
The distance travelled by a particle starting from rest is plotted against the square of the time elapsed from the commencement of motion. The resulting graph is linear. The slope of this graph is a measure of
D
The lower and upper fixed points marked on a mercury-in-glass thermometer are 210mm apart. The end of the mercury column in the tube is 49mm above the lower fixed point in a room. What is the temperature of the room in degrees Celsius?
B
A given mass of an ideal gas occupies a volume V at a temperature T and under a pressure P. If the pressure is increased to 2P and the temperature reduced to ½T, then the percentage change in the volume of the gas is
C
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