ML AGGARWAL CLASS 8 Chapter 18 Mensuration Exercise 18.3
Exercise 18.3
Question 1
Sol :
Given volume of cube =343 cm3
Let 'S' be edge of cube
Volume of cube = S3
s3=343S=3√343S=7 cm.
ஃ Length of an edge of cube = 7cm
Question 2
Sol :
(i) Volume of Cuboid 90 cm3
Length 6cm , Breadth 5cm , Height 3cm
(ii) Volume of cuboid 840 cm3
Length 15cm , Breadth 15cm , Height 7cm
(iii) Volume of Cuboid 62.5 m3
Length 10m , Breadth 5m , Height 1.25m
Question 3
Sol :
Given
Volume of cuboid =312 cm3
Base Area=26 cm2
volume =312 cm∘
Area × height =312
26×h=312
h=31226
h = 12cm
Question 4
Sol :
Given
Godown dimension (1×b×h)= 55 m×45 m×30 m
Cuboidal box volume =1.25m3
godown volume =l×b×h=55×45×30=74250 m3
No. of Cuboidal boxes = godown Volume box volune
=742501.25
No. of cuboidal boxes =59400
Question 5
Sol :
Given Dimension of rectangular pit = 1.4 m×90 cm×70 cm
Volume of pit = l×b×h
=140×90×70 cm3
Volume of pit = 882000 cm3
Given
Brick dimension (l × b) =2.1 cm×10.5 cm
Let 'h' height of brick
1000× Brick volume = pit volume
1000× 21×10.5×h=882000
h=88200021×10.5×1000
h=4cm
∴ Height of brick =4 cm
Question 6
Sol :
Let 'a' be edge of cube
Volume of cube = a3
If each edge of cube is tripled = a1=3a
Volume of new Cube = a13
=(3a)3
=27a3
The Volume becomes 27 times the original Volume of Cube.
Question 7
Sol :
Given
Milk tank is in the from of cylinder
Diameter of tank = 1.4m × 2
Height of tank = 8m
Volume of tank = πd2×h
π×(1−4)2×8
Volume of tank = 49 .260m3
∴ Volume of tank = 49.260 lit
Question 8
Sol :
Given
Extended dimension of box = 84 cm×75 cm×64 cm
Thickness of box = 2 cm
∴ Internal Dimension of box = (54−2×2)cm , (75 - 2 × 2) cm ,(64- 2×2) cm
=80 cm×71 cm×60cm
Volume of wood = External Volume - Internal Volume
= (84×75×64)−(80×71×60)
403200−340800
Volume of wood =62400 cm3
Question 9
Sol :
Given
Two Cylinder jar has same volume
Let
d1,d2 are diameter jar
h1,h2 are heights of jar
Given
d1:d2⋅3:4
Volume of cylinder equal
∴ π4d21×h1=π4d22×h2
d21×h1=d22×h2
(d1d2)2=h2h1
(34)2=h2h1
h1h2=169
h1:h2=16:9
∴ Height of cylinders are in the ratio = 16: 9
Question 10
Sol :
Let 'r' be the ratio's of cylinder
h be the height of cylinder
Volume V = πr2×h
Now radius is =R1=r2
Height is doubled = h1=2h
New Volume V1=πr21×h1
=π(r2)2×(2h)
=πr24×2h
v1=πr2×h2
v1=v2
ஃ New Volume is half of original Volume
Question 11
Sol :
Dimensions of tin sheet =30 cm×18 cm
When rolled along its length (30cm)
-----------------------------------------------
2πr=30,h=18Cmr=302πr=4.77 cm
Volume =πr2×h=π×4.772×18 Volume =1289.155 cm3
When rolled along breadth (18cm)
----------------------------------------------
2πr=18,h=30 lm
r=182π
r= 2.86 cm
Volume =πr2×h=π×2.862×30=773.493 cm3
Question 12
Sol :
(i) Given dis of pipe = 7cm = 0.07m
Velocity = 5m\sec
Discharge = Area × Velocity
=πd24×V
=π×(0.07)24×5
Discharge =0.0192 m3/sec
∴ Discharge =19.2 lits / see =19.2×60 lits /min
Discharge = 1154 .53 lits\min
Discharge ≈1155lit/min
(ii) Dimension of tank = 4m×3m×2.31m
Discharge =0.0192 m3/sec
1.154 m3/min
Time taken to fill the tank = Volume of tank Discharge
=4×3×2.311.154
Time taken to fill the tank = 24min
Question 13
Given
Vessel 1
radius 15cm
Height 40cm
Volume πxr2×h
π×(15)2+40
Volume 28274.33 cm3
Vessel 2
Radius 20cm
Height 40cm
Volume πxr2×h
π×(20)2+45
Volume 56548.667 cm3
Given
Another vessel with capcity equal to sum of vessel 1 and vessel 2
Let radius of vessel's = R
Height of vessel = 30cm
(πR2)×30=28274.33+56548.667
30×(11R2)=84823R2=84823π×30
R2=900
R=√900
R=30Cm
∴ Radius of vessel = 30cm
Question 14
Sol :
Given
Pole height = 7m
Pole diameter = 20cm = 0.2m
Density = 225 kg/m3
Volume of wood = πd24×h
=π4(20)2104×7
Volume of wood =0.219 m3
Weight of wood = 49.48kg
Question 15
Sol :
A cylinder with diameter of 14cm and height of 30cm is the maximum Volume
That can be cut from given Cuboid
Volume of cylinder = π4d2×h
=π4(14)2×30
Volume of cylinder = 4618.14 cm3
Volume of wood wasted = Volume of cuboid - Volume of cylinder
= 14×14×30−(4618.14)
Volume of Wood wasted = 1261.85 cm3
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