WAEC 2019 - PHYSICS ANSWER

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PHYSICS OBJ:
1-10: CBBBCACBCB
11-20: CCCABBBDCD
21-30: CCDADCDDDA
31-40: BDDBBCAABC
41-50: ABDABDBCBA
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ANSWERS:

(1)
Mass = 20g = (20/100)kg = 0.02kg
Extension = 5cm = (5/100)m = 0.05m
K = 200N/
V = ?
1/2mv² = 1/2ke²
V = √ke²/m = √200×0.05×0.05/0.02
V = √25
V = 5m/s



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(2a)
P is initial velocity in m/s
β is angle of projection
H is maximum height
R is Range

(2b)
R = P²sin2β/g
at maximum range, sin2β = 1
=> Rmax = p²/g
This happens at β = 45degree
name



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(3)
(i) Photoelectricity
(ii) Thermonic equation
(iii) Compton effect

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(4)
(i) magnetic declination
(ii) magnetic inclination
(iii) horizontal components

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(5a)
Free eletcron: These are electrons which are not attached to an atom. They are mobile electrons which are free for bonding.

(5b)
Holes are spaces left by electrons in an atom in a crystal lattice. They are positively charged.

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(6a)
Principle of operation of fiber optics state that the density of transparent glass and the refractive index is greater than the density of the two mirrors. It makes use of the principle of the total internal reflection.

(6b)
(i) It is used to view deep down the throat of a patient
(ii) It is used to conveying information

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(8ai)
It state that every particles in the universe attract every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them

(8aii)
Gravitational field is a region of space around a mass on which the gravitational force of the mass can be felt

(8bi)
F=GMeM/re² ------from newton's law
Where Me is mass of earth
re is the distance of mass from earth
G is a constant of gravitation
But F=GMeM/re² =mg
Me=GMe/re²=g
g=GMe/re²

(8bii)
(i)That The earth is a sphere
(ii)That g depends on mass of earth alone

(8c)
Using F = GMeM/r²
F=6.67*10^-11*5.98*10²4*2.00*10³degree/(1.50*10^8*10³)²
F= 79.7732*10^43/2.25*10²²
F=35.455*10²1
=3.5455*10²2N

(8di)
Escape velocity (Ve) is the minimum velocity required for an object (egg statelite) to just escape or leave the gravitational influence or field of an astronomical body (eg earth) permanently
(8dii)
(i)g varies across the earth but G is constant
(ii)the unit of g is m/s² while that of G is NM²/Kg²


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(9ai)
Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process.

(9aii)
(i)surface area in contact with atmosphere
(ii)nature of the liquid

(9bi)
The rate of absorption of heat by clay pot is less than the rate of absorption of heat by plastics. Also, water gets evaporated in a clay pot which the evaporation causes cooling; so water in a clay pot remains cool

(9bii)
An increase in pressure in the cooker increase the ambient temperature in the cooker hence the food cooks faster

(9c)
(i) Change in the state of a substance
(ii) Increase in temperature

(9di)
Heat supplied = m1
lvt = m1
12*40*1400=1.5*1
L=12*40*1400/1.5
L=672000/1.5= 448,000J/kg
Laten heat of fusion of the body = 4.48*10^5J/Kg

(9dii)
lvt=mc D tita
12*40*72=1.5*c*60
C=12*40*72/1.5*60
C=384J/Kg/K
Specific heat capacity of the body =384J/Kg/K



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(11ai)
Force is anything that causes motion.Its S.I unit is Newton(N) or Kgm/s²

(11aii)
(i) Static friction
(ii) Dynamic friction

(11bi)
DRAW THE GRAPH

(11bii)
Deceleration
during last 5s=18/5=3.6m/s²

(11biii)
Total distance=S1+S2+S3+S4
=(30*20)+1/2(18+30)(6)+(18*10)=(1/2*5*18)
=600+144+180+45
=969metres




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ANSWER COMPLETED
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