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## 2020 WAEC GCE Physics Theory and Obj Answer

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2020 WAEC GCE Physics Theory and Obj Answer by : 1:50 am On January 27, 2020

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### Past WAEC GCE 2018 Physics Theory and OBJ Answers

Physics OBJ:
1-10: ABABDBBBBC
41-50: BDAACAABCA

(1)
(a)
Horizontal speed just before it strikes floor = ucosθ
= 10cosθ * 1.0
= 10 m/s

(b)
t = √(2g/h)
= √(2*10*1)
= √20
= 4.47s

(2)
(i)cutting through materials,such as metal.
(ii)burning,eg laser engraving.
(iii)It is used to destroy damaged tissue or to stop bleeding, eg after surgery.

(3)
(i)Iron
(ii) Nickel
(iii) Cobalt

(4a)
Given: u = 20m/s
t = 4s
g = 10m/s²
h = ?
Using s = ut – ½gt²
s = 20(4) – ½(10)(4)²
s = 0m

(b)
The inference is that after 4s, the ball returns back to the plane of projection

(5)
(i) Cost
(ii) Temperature Co-efficient
(iii) Size and Watts Capacity.

(8ai)
Force is a push or pull which changes a body’s state of rest or uniform motion in a straight line.

(8aii)
(i) field force
(ii) contact force

(8bi)
Bodies are designed to move through fluid streamlined in shape so as to oppose or overcome the motion of the fluid

(8bii)
(i) fish
(ii) submarine

(8ci)
Mass= 1.3 kg
F= 1.2 m
V= 7.0 m/s

[Diagram]

(8cii)
(a) Acceleration
Note , V²= U² + 2as
Where S=r=1.2 m
(7.0)²= 0²+2× a (1.2)
= 49/2.4 = 2.4a/2.4
a = 20.4

(b)
Force=?
From force = MA
Force =1.3×20.4
Force =25.52

(9a)
(i) Coat (Trapped air in between the fabric)
(ii) The hair and the fur of animals are bad conductors of heat and they protect them from cold .

(9b)
-Renewable: Water, corn stalk
-Non-renewable: coal, natural gasgas

(9c)
A closed is a physical system so far removed from other systems that it does not interact with them.

(9d)
Heat required to melt = mc∆ + ml
NB: Not sure of the temperature given, if it is -3°C or -5°C, However, Using -3°C
Heat = (0.1×2200×3)+(0.1×2.26×10^6)
= 226660 J

(9ei)
Given: 75 heart beats in 1 min
Therefore in 1 hour, we have (75×60) heart beats = 4500 heart beats
Also given: 2J of energy is expended in 1 heart beat
Therefore for 4500 heart beats, energy expended = (4500×2) J = 9000J

(9eii)
Energy = mc∆
9000 = (0.25×4200×∆)
9000 = 1050∆
∆ = 9000/1050
Temperature rise = 8.57°C

(10a)
(i) Plane waves
(ii) Spherical waves
-For plane waves -Their dipper are wooden strip
-For spherical wave – Their dipper are spherical ball

(10b)
White and are actual colours of light because both white and black are centralof additive and substractive

(10c)
A yellow object is illuminated with green liight and when viewed through a yam filter becomes white since the colours consist of both primary and secondary colours which are known as complementary colours

(10d)
f0=V/2l
2f0l=V
l=V/2f0
=330/(2*400)
l=330/800
0.41m

(10e)
f=200khz
Period T=1/f
T=(1/200*10^3)s
Period T=5*10^-6s

(11a)
(i) Electrical method
(ii) Contact method

(11b)
Electric lines of force are imaginary lines drawn in an electric field in such a way that the direction at any point gives the direction of the electric field at such a point

(11c)
QR = SP

(11d)
Resistivity is the resistance of a unit length of material of unit cross-sectional area

(11d)
Heat required to melt = mc∆ + ml
NB: Not sure of the temperature given, if it is -3°C or -5°C, However, Using -3°C
Heat = (0.1×2200×3)+(0.1×2.26×10^6)
= 226660 J

(11e)
Given: F = 50Hz
L = 10 mH (10×10^-³H)
Inductive reactance, XL = 2πFL
= 2×3.14×50×10×10^-³
= 3.14 ohms

(11f)
If voltmeter reads 12V, over the 500 ohms, then using I = V/R
current in the circuit is I = 12/500
I = 0.024A
Hence over the 200 ohms, V = IR
V = 0.024×200
V = 4.8 VOLTS