Examples: Surface Area Video Lecture - CTET & State TET

hello friends this video on the
insulation part 12 is brought to you by
SRAM pure calm no more fear from exam
perfume based on whatever we have learnt
about the surface areas of different
solid shapes let's try out a few
questions question number one looks are
painted the outside of the cabinet of
vision one meter by 2 meter by 1.5
meters how much surface area did she
cover if she painted all except the
bottom of the cabinet so basically we
need to find out the total surface area
of this cabinet except the bottom so we
just need to exclude the bottom so for
that what do we need to do we need to
find out the total surface area of this
cabinet now what is the shape of this
cabinet here the cabinet is in the shape
of a cuboid because length drapes and
Heights are different so here if you see
light is equal to 2 meters depth is
equal to 1 Newton and height is equal to
1.5 meters right so do you have to find
out the total sub search surface area
and subtract from that the area of the
bottom that is the area of the base set
B so how do we do that the total surface
area of a cuboid is equal to 2 into L B
plus B 8 + n 8 and what would be the
area of the bottom to the bottom surface
for the bottom circle the length would
be N and red 2 would be V so this would
be n into B so this is 2 into n into B
plus B into H plus n into H minus n into
D so this is equal to 2 into 2 plus 1.5
plus 3 minus 2 this is equal to 2 into 6
point 5 minus 2 that is equal to 13
minus 2 which is equal to 11
square so this is the total surface area
that she has covered question number two
a floral in Drupal tank of radius seven
meters and height three meters is made
from a sheet of metal
how much sheet of metal is required so
here you have to read the question very
carefully close cylindrical stance that
means the top and the bottom they are
closed so you have those two surfaces
and then so you have to consider total
surface area here so the radius is given
as seven meters and also the height of
this cylinder is given as 3 meters okay
so let us now find it out so I think the
image is not as per the question which
is mentioned in the question the ladies
will move and the height is smaller so
any little so just to give you an idea
about how it might look
the radiation 7 meters and height is 3
meters so total surface area of a
cylinder is equal to 2 PI I into I plus
h so that is equal to 2 into 22 by 7
into seven it is seven plus three so the
seven and seven will get cancelled so
this is 44 into 7 plus T that is equal
to 44 into 10 which is equal to 440
meter square so this much area of the
sheet of metal would be required
question number three a road roller
takes 750 complete revolutions to move
one over to level a road find the area
of the road if the diameter of the road
roller is 84 centimeters and the length
is one region now when you look at the
road roller
you see it is in the shape of a cylinder
where this is the radius of the cylinder
and this is
the height of the cylinder right so this
would be your radius and this would be
your height so this is like a cylinder
now one complete revolution of this road
order that means if you start so if the
roller starts from here and it is a
state till it again reaches to the same
point so that is one complete revolution
so such one complete revolution of the
road roller would actually means the
baptism surface area of the roller so
when it completes one revolution it
cupboards area that is equal to the
total lateral surface area of the
cylinder right because you see in one
revolution what is happening it starts
from here and it reaches here thank so
in one revolution it covered that much
area which is the area of death which is
the natural surface area of the curve
circuit area of the rollers so let us
try to find out the lateral surface area
of the road rollers which is given by 2
pi RH now in this problem radius is
given as radius is not even diameter is
given as 84 centimeters so if diameter
is 84
then radius would be 84 divided by 2
which is equal to 42 centimeters okay so
2 into 5 is 22 by 7 radius is 42
centimeters and height is 1 meters
because length of the road roller is
nothing but the height so - band meters
now here what we do is taken in
centimeter selective event also in
centimeter so this will be 100
centimeters vii speak to the 42 so this
will be equal to 2 6 4 0 0 centimeters
squared this is equal to 2 point 6 4
meter square so this is the natural
surface area of the roller now we have
to find out the area of the road now the
question is that in 750 revolutions it
covers the entire
you're loaded so one revolution it
covers this much area so that means in
750 revolutions how much area it will
cover 750 into two point six foot so
this much area it will cover which is
equal to one nine eight zero meter
square so this is nothing but the area
of the road so I hope you understood the
problem so see one revolution that means
in one revolution it covers the toes and
natural surface area of this cylinder
right so we calculate with the natural
surface of the cylinder now in 750
revolutions it covers the entire area of
the road so in 750 revolutions it will
cover how many assailing to speak into
the national central area which is one
nine eight zero meters and that's the
area of the road which is covered
question of the scope a suitcase which
measured with measures 80 centimeter by
48 centimeters by 24 centimeters is to
be covered with a black ball in clothes
how many millions of clothes of which 26
centimeters is required to cover hundred
such suitcases now what is the shape of
the shoe T so the suitcase is in the
shape of a Q white right so then nail
integrates and height of the cuboid is
given as 80 48 and 24 respectively now
when you want to cover this complete
suitcase with a closed that means you
need to know the total surface area of
the suitcase so let us calculate the
total surface area of this cuboid which
is given by 2 into L D plus BH plus and
H so this is equal to 2 into dental 80
breathless 24 again breakfast 24 5 is 48
again 1980 and - 48 so let us calculate
this this is 2 into 1 9 2 0 plus 1 1 5 2
+ 3 8 4 0 this is equal to 1 3 8 2 4
centimeter square this is 1
point t 8 to 4 meter square so this is
the total that is area of the suitcase
so therefore how much clothes will be
needed to cover this suitcase so we can
see that the area of clothes needed to
cover one chute is because right now we
have calculated the total area of 150 so
no Haven is the total that behavior of
one such case that much area of clothes
will be needed to cover it so now we
have to find out the length of the
clothes needed to cover it because width
of the closes already given the area of
the float will be length into breadth
which is equal to one point three eight
to port therefore length of the load
would be one point three eight to four
divided by thread orbit which is given
as 96 centimeters which can be written
as point nine meters so this is equal to
one point four four meters so we need
one point four four meters of clothes to
cover one suitcase but in the question
it is asking for 100 sheet pieces so 100
suitcases the lens will also get
multiplied by hundred so you get 144
meters so we need 144 meters of clothes
of width 96 centimeters to cover hundred
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