# 2021 WAEC MAY/JUNE PHYSICS Questions & Answers: 2020 WAEC MAY/JUNE PHYSICS ANSWERS Night before Exam

Friday 28th August 2020
Physics 2 (Essay) – 9:30am –11:00am
Physics 1 (objective) – 11:00am –12:15pm

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PHYSICS OBJ
1-  10: DCCAACDCCC
11-20: BDBABBACAC
31-40: BDDDDACCCA
41-50: CAAABBCBBC

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==No. 12  completed==

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(1)
Original length Lo = 3m
extension e = 3Lo = 3×3 = 9m
F ∝e
F = ke where k = 982.3Nm‐²
F = 982.3×9 = 8840.7N
The force that produces the extension F = 8840.7N

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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(2a)
Metal flat plate: It is a collector of heat that converts the radiant solar energy from the sun into heat energy by the process of greenhouse effect.

(2b)
Thermal Insulator: It prevents loss of accumulated heat in the solar collector and thereby improves its absorption efficiency.

(2c)
Tubes: They are used to capture almost all the sun's energy. It is the most efficient solar collector

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

(3a)
Plastic

(3b)
The refractive index of the core must be greater than that of the cladding.

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

(4)

V ∝ T^x U^y
LT‐¹ ∝(MLT^‐²)^x(ML^‐1)^y
LT‐¹ ∝ M^xL^xT^‐²x × M^yL^-y
LT‐¹ ∝ M^(x+y) L^(x-y) T^‐²x
Comparing
X-y = 1 -----(1)
X+y = 0 -----(2)
-2x = -1 ----(3)
From equation 3,
X = 1/2
Putting X = 1/2 into eqn 2
y = -1/2
Equation is:
V ∝ T½ U‐½
V = √T/U
V = K√T/U
Where k is constant

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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(5)
Work done in a gravitational field = force × distance
= f × r
= GMeM/R² × R
= GMeM/R
Work done is also kinetic energy, K.E = 1/2MVe²
Equating both
GMeM/R = 1/2MVe²
Ve² = 2GMe
Ve = √2GMe/R -----(1)
Also,Force f = GMeM/R² = mg
Me = gR²/G -----(2)
Putting (2) into (1)
Ve = √2GgR²/GR = √2gR

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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(6)
θ = 30°, g = 10m/s²
Time of flight, T = 25seconds
Using,
Time of flight, T = 2usinθ/g
25 = 2usin30°/10
2u(0.5) = 250
u = 250
Velocity of projection, u = 250m/s

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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(7)
(i)Coherence
(ii)Directionality
(iii)Monochromatic

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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(8ai)
A torque is defined as a measure of the force that can cause an object to rotate about an axis

(8aii)
Factors that determine torque are;
- The magnitude of the force
- The angle between the force and the lever arm

(8bi)
Freefall simply means the act of which are objects fall freely under the influence of gravitational force. An object under free fall does not encounter air resistance

(8bii)
Height of tower H = 40.0m
Velocity v = 10.0m/s, time t= ? , g=10.0m/s

Using the relation
S= ut + 1/2gt^2
H= ut + 1/2gt^2
40= 10t + 1/2*10t^2
4= t + t^2/2
= t^2 + 2t - 8=0 ( solving quadratically)
= (t+4)(t-2)=0
t+4=0 or t-2=0
t= -4 or t=2

Therefore the time to fall on the ground t=2s

(8c)
Side of the cube of wood = 8.0cm
2.0cm = 1/4 of the side immersed in water
R.density of water Rw = 1.00
R.density of Oil = Ro = 0.72
Volume of the wood V = L³
= 8×8×8
V = 512cm³
Volume immersed in water = 1/4×512 = 128cm³
Weight of water displaced = 128g × Rwater = 128×l
By applying the principle of flotation
Mass of wood = 128×Rw
=128 × l = 128g

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
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2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

(10ai)
The critical angle is defined as the angle of incidence in the denser medium when the angle of refraction in the dense medium is 90°

(10aii)
The conditions necessary for total internal reflection to occur
1. The light must be travelling from an optically more dense to an optically less dense medium.
2. The angle of incidence in the denser medium must be greater than the critical angle.

(10aiii)
Three practical applications of total internal reflection:
[Choose three]
(i) Mirages
(ii) Field of view of fish underwater.
(iii) Refractometer.
(iv) Optical fibre.
(v) Binoculars.

(10b)
Two effects of refraction:
(i) The apparent depth of a swimming pool.
(ii) Apparent bending of a stick partly immersed in water.

(10ci)
Progressive wave is defined as a wave that transfers energy in travelling or moving away from the source of the disturbance.

(10cii)
y = 0.5sin(1000πt - 100πx)/17 = y = Asin(2πx/λ - wt)

(∝) at = 1000πt
===》 w = 1000
But w = 2πf
2πf = 1000π
f = 1000/2
f = 500Hz

(β) 2πx/λ = 100π/17 x
2/λ = 100/17
λ = 2×17/100
=0.34m

(γ) V = fλ
= 500 × 0.34
=170m/s

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

(12)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE PHYSICS Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

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Updated At: April 17th 2021, (06:04:05)