JAMB Physics Previous Year Questions: 2021 | Physics for JAMB PDF Download

Q1: The slope of the straight line displacement-time graph indicates?
(a) distance traveled
(b) uniform velocity
(c) uniform acceleration
(d) uniform speed
Ans: (b)
Uniform velocity = Δs/Δt

Q2: A man will exert the greatest pressure when he?
(a) lies flat on his back
(b) lies on his belly
(c) stands on both feet
(d) stands on the toes of one foot
Ans: (d)
Pressure is inversely proportional to A, hence

Q3: Which of the following physical quantities units are derived?
I. Area
II. Thrust
III. Pressure
IV. Mass
(a) I, II, III and IV
(b) I, II, and III only
(c) I, II, and IV only
(d) I and IV only
Ans: (b)

Q4: A ball of mass 0.5kg moving at 10ms⁻¹ collides with another ball of equal mass at rest. If the two balls move off together after the impact, calculate their common velocity.
(a) 0.2ms⁻¹ 
(b) 0.5ms⁻¹ 
(c) 5.0ms⁻¹ 
(d) 5.5ms^-1
Ans: (c)
m₁ u₁ + m₂ u₂ = (m₁ + m₂)v
m₁ = 0.5kg, u₁ = 10ms¹ , m₂ = 0.5kg, u₁ = 0
∴ (0.5kg x 10) + (0.5 x 0) = (0.5 + 0.5)v
v = 5ms¹ 

Q5: The motion of a body is simple harmonic if the?
(a) acceleration is always directed towards a fixed point
(b) path of motion is a straight line
(c) acceleration is proportional to the square of the distance from a fixed point
(d) acceleration is constant and directed towards a fixed point
Ans: (a)
In mechanics and physics, simple harmonic motion is a special type of periodic motion where the restoring force on the moving object is directly proportional to the magnitude of the object's displacement and acts towards the object's equilibrium position.

Q6: Which of the following is not correct about the molecules of a substance in a gaseous state? They
(a) are in a constant state of motion
(b) have different speeds
(c) have a temperature which is measured by the average kinetic energy
(d) The collision between the gases is perfectly inelastic
Ans: (d)
All collisions between gas molecules are perfectly elastic; all kinetic energy is conserved. When cars collide, energy is lost to bending bumpers and metal. Molecules do not act like this. Instead, they act like billiard balls.

Q7: A given mass of gas has a pressure of 80 Nm⁻² at a temperature of 47 C. If the temperature is reduced to 27 C with volume remaining constant, the new pressure is?
(a) 46.0 Nm⁻² 
(b) 75.0 Nm⁻² 
(c) 80.0 Nm⁻² 
(d) 85.3 Nm⁻²
Ans: (b)

P₁ = 80Nm² 
T₁ = 47 + 273 = 320k
T₂ = 27 + 273 = 300k
P₂ ?


Q8: 0.5kg of water at 10ºC is completely converted to ice at 0ºC by extracting (88000) of heat from it. If the specific heat capacity of water is 4200jkg¹ Cº. Calculate the specific latent heat of fusion of ice.
(a) 9.0kjkg⁻¹ 
(b) 84.0kjkg⁻¹ 
(c) 134.0kjkg⁻¹ 
(d) 168.0kjkg⁻¹
Ans: (c)
Given
Heat(H) = 88,000J,
Mass(M)= 0.5kg,
Specific heat capacity of water(C) = 4200JkgºC,
Specific latent heat of fusion(L) = ?,
Temperature change(??) =  ?2 -  ?1 =  (10 - 0)° = 10°
H = MC?? + ML


Q9: Which of the following instruments may be used to measure relative humidity?
(a) Hydrometer
(b) Manometer
(c) Hygrometer
(d) Hypsometer
Ans: (c)
A hygrometer is an instrument used to measure the amount of water vapour in the air, soil, or confined spaces. Relative humidity (RH) is a measure of the amount of water vapor in a water-air mixture compared to the maximum amount possible.

Q10: A source of sound produces waves in air of wavelength 1.65m. If the speed of sound in air is 330ms⁻¹, the period of vibration in air is?
(a) 200
(b) 0.005
(c) 0.5
(d) 0.02
Ans: (b)
v = λ/T
v = 330ms^-1
λ = 1.65m
330 = 1.65
T = 1.65/330 = 0.005s

Q11: A boy standing some distance from the foot of a tall cliff claps his hands and hears an echo 0.5s later. If the speed of sound is 340ms⁻¹, how far is he from the cliff?
(a) 680m
(b) 170m
(c) 34m
(d) 85m
Ans: (d)


Q12: Which of the following is not a vector quantity?
(a) momentum
(b) force
(c) temperature
(d) displacement
Ans: (c)
Vector quantities are physical quantities characterized by the presence of both magnitude and direction. Examples of vector quantities are displacement, force, torque, momentum, acceleration, velocity, etc.
Scalar is a physical quantity that is completely described by its magnitude. Examples of scalars are speed, density, volume, energy, mass, time, etc.

Q13: Calculate the heat energy required to vaporize 50g of water initially at 80ºC if the specific heat capacity of water is 4.23jg⁻¹ k⁻¹ (specific latent heat of vaporization of water is 2260jg − 1
(a) 530000J
(b) 23200J
(c) 17200J
(d) 130000J
Ans: (d)
H = mc Δθ + mL
m = 50g, c = 4.23J/gk,L = 2260, Δθ = 80ºC
H = 50 [4.23 x 80 + 2260]
= 129920 ≈ 130,000J

Q14: In a series R-L-C circuit at resonance, the voltages across the resistor and the inductors are 30V and 40V respectively. What is the voltage across the capacitor?
(a) 30V
(b) 40V
(c) 50V
(d) 70V
Ans: (b)
AT resonance; X_L = X_c
V_L = V_c = 40V

Q15: If the frequency of an emitted x-ray is 1.6 x 10¹⁶ Hz, the accelerating potential is?
[e = 1.6 x 10^{− 19} J, h = 6.63 x 10^-34 Js]
(a) 6630.0V
(b) 663.0V 
(c) 66.3V
(d) 6.6V
Ans: (c)
Given:



Q16: If the fraction of the atoms of radioactive material left after 120 years is 1/64, what is the half-life of the material?
(a) 24 years
(b) 20 years
(c) 10 years
(d) 2 years
Ans: (b)
Given fraction of the atoms left = 1/64

= 20 years

Q17: A certain radioactive source emits radiation that was found to be deflected by both magnetic and electric fields. The radiation is?
(a) beta rays
(b) gamma rays
(c) x-rays
(d) ultra-violet rays
Ans: (a)
Because Alpha is positively charged and Beta is negatively charged, they are deflected in an electric or magnetic field, whereas Gamma radiations are not charged and as a result do not deflect in an electric or magnetic field.

Q18: The inner diameter of a test tube can be measured accurately using a?
(a) micrometer screw gauge
(b) pair of dividers
(c) meter rule
(d) pair of vernier calipers
Ans: (d)
Vernier callipers are used to measure the internal and external diameters of a tube

Q19: Two bodies have masses in the ratio3:1. They experience forces which impart to them, acceleration in the ratio 2:9 respectively. Find the ratio of forces the masses experienced
(a) 1:4
(b) 2:1
(c) 2:3
(d) 2:5
Ans: (c)


Q20: Particles of mass 10⁻² kg is fixed to the tip of a fan blade which rotates with angular velocity of 100rad⁻¹. If the radius of the blade is 0.2m, the centripetal force is?
(a) 2N
(b) 20N
(c) 200N
(d) 400N
Ans: (b)
Given: m = 10⁻² 
w = 100rads⁻¹ 
F = mw² r
r = 0.2
m = 10⁻² x (100)² x 0.2
= 20N

Q21: A lead bullet of mass 0.05kg is fired with a velocity of 200ms⁻¹ into a block of mass 0.95kg. Given that the lead block can move freely, the final kinetic energy after impact is?
(a) 50J
(b) 100J
(c) 150J
(d) 200J
Ans: (a)
Given:
m₁ = 0.05kg, u₁ = 200ms⁻¹ , m₂ = 0.95kg

m₁u₁ = v(m₁ + m₂) [law of conversation of momentum]


Q22: A ball of mass 0.1kg is thrown vertically upwards with a speed of 10ms⁻¹ from the top of a tower 10m high. Neglecting air resistance, its total energy just before hitting the ground is? (Take g = 10ms⁻²)
(a) 5J
(b) 10J
(c) 15J
(d) 20J
Ans: (c)
Given:
m = 0.1kg
u = 10ms⁻¹ 
h = 10m
g = 10ms^-2  
At h_max v = 0

v² = u² - 2gh
0² = 10² - 2 x 10h
20h = 100
h = 5m
Total Height = 10 + 5
= 15m
Total Energy = mghr = 0.1 x 10 x 15
= 15J

Q23: A car of mass 800kg attains a speed of 25m/s in 20secs. The power developed in the engine is?
(a) 1.25 x 10⁴ W
(b) 2.50x 10⁴ W
(c) 1.25 x 10⁶ W
(d) 2.50 x 10⁶ W
Ans: (b)

2.5 x 10⁴W

Q24: When the breaks in a car are applied, the frictional force on the tyres is...?
(a) a disadvantage because it is in the direction of the motion of the car
(b) a disadvantage because it is in the opposite direction of the motion of the car
(c) an advantage because it is in the direction of the motion of the car
(d) an advantage because it is in the opposite direction of the motion of the car
Ans: (d)
The frictional force opposes the motion. Friction braking is the most commonly used braking method in modern vehicles. It involves the conversion of kinetic energy to thermal energy by applying friction to the moving parts of a system. The friction force resists motion and in turn generates heat, eventually bringing the velocity to zero. 

Q25: If the stress on a wire is 10⁷ NM⁻² and the wire is stretched from its original length of 10.00m to 10.05m. The young's modulus of the wire is?
(a) 5.0 x 10⁻⁴ Nm⁻² 
(b) 5.0 x 10⁻⁵ Nm⁻² 
(c) 2.0 x 10⁻⁸ Nm⁻² 
(d) 2.0 x 10⁹ Nm⁻² 
Ans: (d)
Young's modulus (E) is a property of the material that tells us how easy it can stretch and deform and is defined as the ratio of tensile stress (?) to tensile strain (?). Where stress is the amount of force applied per unit area (? = F/A) and strain is extension per unit length (? = dl/l).


Q26: A solid weighs 10.00N in air, 6N when forcefully immersed in water, and 7.0N when fully immersed in a liquid, X. Calculate the relative density of the liquid X.
(a) 5/3
(b) 4/3
(c) 3/4
(d) 7/10
Ans: (c)



Q27: When the temperature of a liquid increases, its surface tension
(a) decreases
(b) increases
(c) remains constant
(d) increases then decreases
Ans: (a)
An increase in temperature lowers the net force of attraction among molecules and hence decreases surface tension;  soap decreases the pull of surface tension.

Q28: A gas at a volume of V₀ in a container at pressure p₀ is compressed to one-fifth of its volume. What will be its pressure if the magnitude of its original temperature T is constant?
(a) p₀/5
(b) 4p₀
(c) p₀
(d) 5P₀
Ans: (d)


Q29: A piece of substance of specific heat capacity 450Jkg⁻¹ k¹ falls through a vertical distance of 20m from rest. Calculate the rise in temperature of the substance on hitting the ground when all its energies are converted into heat. [g = 10ms⁻²]
(a) 2/9 ºC
(b) 4/9 ºC
(c) 9/9 ºC
(d) 9/4 ºC
Ans: (b)
According to the law of conservation of energy, energy states that energy can neither be created nor destroyed - only converted from one form of energy to another.
mc Δθ = mgh
Δθ = gh/c

= 4/9 ºC

Q30: I. A liquid boils when its saturated vapor pressure is equal to the external pressure
II. Dissolved substances in pure water lead to an increase in the boiling point.
III. When the external pressure is increased, the boiling point increases.
IV. Dissolved substances in pure water decreases the boiling point
Which of the above combinations are peculiarities of the boiling point of a liquid?
(a) I, II and III only
(b) I, II, III, and IV
(c) I, II, and IV
(d) II, III, and IV
Ans: (a)
The boiling point of a liquid depends on temperature, atmospheric pressure, and the vapour pressure of the liquid. Boiling begins when the atmospheric pressure is equal to the vapor pressure of the liquid.

Q31: The temperature gradient across a copper rod of thickness 0.02m, maintained at two temperature junctions of 20º and 80ºC respectively is?
(a) 3.0 x 10² km⁻¹ 
(b) 3.0 x 10³ km⁻¹ 
(c) 5.0 x 10³ km⁻¹ 
(d) 3.0 x 10⁴ km⁻¹ 
Ans: (b)

3.0 x 10³ km⁻¹   

Q32: Calculate the mass of ice that would melt when 2kg of copper is quickly transferred from boiling water to a block of ice without heat loss (specific heat capacity of copper = 400Jkg¹ k⁻¹, latent heat of fusion of ice = 3.3 x 10⁵ Jkg⁻¹)
(a) 8/33 kg
(b) 3.3/80 kg
(c) 80/33 kg
(d) 3.3/8 kg
Ans: (a)
mcΔθ = m λ f
2 x 400 (100 - 0) = m(3.3 x 10⁵)  


Q33. The equation of a wave traveling along the positive x-direction is given by; y = 0.25 x 10⁻³ sin (500t - 0.025x). Determine the angular velocity of the wave motion.
(a) 0.25 x 10⁻³ rads⁻¹ 
(b) 0.25 x 10⁻¹ rads⁻¹ 
(c) 5.00 x 10² rads⁻¹ 
(d) 2.50 x 10³ rads⁻¹     
Ans: (c)
y = A sin (wt + 0)
y = 0.25 x 10⁻³ sin (500t - 0.025x)
w = 5.00 x 10² rads^-1   

Q34: If a sound wave goes from a cold air region to a hot air region, its wavelength will...?
(a) increase
(b) decrease
(c) decrease then increase
(d) remain constant
Ans: (a)
When sound travels from hot air to cold air or from cold air to hot air it will refract, the molecules of air are moving faster and the vibrations of the sound wave can therefore be transmitted faster. Hence, the speed of sound is greater in hot air than it is in cold air.

Q35: The lowest note emitted by a stretched string has a frequency of 40Hz. How many overtones are there between 40Hz and 180Hz?
(a) 4
(b) 3
(c) 2
(d) 1
Ans: (b)
f₀ = 40H₃ 
1st overtone = 2f₀ = 80H₃ 
2nd overtone = 3f₀ = 120H₃ 
3rd overtone = 4f₀ = 160H₃ 
4th overtone = 5f₀ = 200H₃ 
Hence, the number of overtones between 40H₃ and 180H₃ = 3

Q36: A man stands 4m in front of a plane mirror. If the mirror is moved 1m towards the man, the distance between him and his new image is?
(a) 3m
(b) 5m
(c) 6m
(d) 10m
Ans: (c)
object distance (u) = image distance (v)
u = 3m
u|v| = 3 + 3 = 6m

Q37: The inside portion of part of a hollow metal sphere of diameter 20cm is polished. The portion will therefore form a?
(a) concave mirror of focal length 5cm
(b) concave mirror of focal length 10cm
(c) convex mirror of focal length 5cm
(d) convex mirror of focal length 10cm
Ans: (a)
f = m/4
= d/4
= 20/4
= 5cm

Q38: The velocities of light in air and glass are 3.0 x 10⁸ ms⁻¹ and 2.0 x 10⁸ ms⁻¹ respectively. If the angle of refraction is 30º, the sine of the angle of incidence is?
(a) 0.33
(b) 0.50
(c) 0.67
(d) 0.75
Ans: (d)

= 0.75

 
Q39: An astronomical telescope is said to be in normal adjustment when the?
(a) eye is accommodated
(b) focal length of an object lens is longer than that of eye piece
(c) final image is at the near point of eye
(d) final image is at infinity
Ans: (d)

Q40: A 2H inductor has negligible resistance and is connected to a 50/π Hz A.C supply. The reactance of the inductor is?
(a) 200Ω
(b) 50
(c) 100/π
(d) 25/πΩ
Ans: (a)