# WAEC 2019 Physics Objective theory Answer PHYSICS OBJ:

.1-10: CBBBBACBCB
11-20: BCCCABBCBA
31-40: BDDBBCAABC
41-50: ABDABDCCBA

COMPLETED..

PHYSICS THEORY: (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

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

(2b)
R = P�sin2β/g
at maximum range, sin2β = 1
=> Rmax = p�/g
This happens at β = 45degree

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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

++++++++++++++++++++++++++++ (8ai)
Terminal velocity is the highest velocity attainable by an object as it falls through a fluid (air is the most common example). It occurs when the sum of the drag force ( Fd ) and the buoyancy is equal to the downward force of gravity (F G ) acting on the object. Since the net force on the object is zero, the object has zero
acceleration .
 In fluid dynamics , an object
is moving at its termin
++++++++++++++++++++++++++++ 9ai)
Latent heat , energy absorbed or released by a substance during a change in its physical state (phase) that occurs without changing its temperature . The latent heat associated with melting a solid or freezing a liquid is called the heat of fusion ; that associated with vaporizing a liquid or a solid or condensing a vapour is called the heat of vaporization . The latent heat is normally expressed as the amount of heat (in units of joules or calories ) per mole or unit mass of the substance undergoing a change of state.

(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

++++++++++++++++++++++++++++ (11ai)
Force is anything that causes motion.Its S.I unit is Newton(N) or Kgm/s^2

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

(11bi)
DRAW THE GRAPH

(11bii)
Deceleration
during last 5s=18/5=3.6m/s^2

(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

COMPLETED..

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