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 = a^{3}
If each edge of cube is tripled = a^{1}=3 a
Volume of new Cube = a^{1^{3}}
=(3 a)^{3}
=27 a^{3}
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 \times 2
Height of tank = 8m
Volume of tank = \frac{\pi}{} d^{2} \times h
\frac{\pi}{} \times(1-4)^{2} \times 8
Volume of tank = 49 .260 m^{3}
∴ Volume of tank = 49.260 lit
Question 8
Sol :
Given
Extended dimension of box = 84 \mathrm{~cm} \times 75 \mathrm{~cm} \times 64 \mathrm{~cm}
Thickness of box = 2 cm
∴ Internal Dimension of box = (54 -2\times 2)cm , (75 - 2 \times 2) cm ,(64- 2\times2) cm
=80 \mathrm{~cm} \times 71 \mathrm{~cm} \times 60 \mathrm{cm}
Volume of wood = External Volume - Internal Volume
= (84 \times 75 \times 64)-(80 \times 71 \times 60)
403200-340800
Volume of wood =62400 \mathrm{~cm}^{3}
Question 9
Sol :
Given
Two Cylinder jar has same volume
Let
d_{1}, d_{2} are diameter jar
h_{1,} h_{2} are heights of jar
Given
d_{1}: d_{2} \cdot 3: 4
Volume of cylinder equal
∴ \frac{\pi}{4} d_{1}^{2} \times h_{1}=\frac{\pi}{4} d_{2}^{2} \times h_{2}
d_{1}^{2} \times h_{1}=d_{2}^{2} \times h_{2}
\left(\frac{d_{1}}{d_{2}}\right)^{2}=\frac{h_{2}}{h_{1}}
\left(\frac{3}{4}\right)^{2}=\frac{h_{2}}{h_{1}}
\frac{h_{1}}{h_{2}}=\frac{16}{9}
h_{1}: h_{2}=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 = \pi r^{2} \times h
Now radius is =R^{1}=\frac{r}{2}
Height is doubled = h^{1}=2 h
New Volume V^{1}=\pi r_{1}^{2} \times h^{1}
=\pi\left(\frac{r}{2}\right)^{2} \times(2 h)
=\frac{\pi r^{2}}{4} \times 2 h
v^{1}=\frac{\pi r^{2} \times h}{2}
v^{1}=\frac{v}{2}
ஃ New Volume is half of original Volume
Question 11
Sol :
Dimensions of tin sheet =30 \mathrm{~cm} \times 18 \mathrm{~cm}
When rolled along its length (30cm)
-----------------------------------------------
\begin{aligned} 2 \pi r &=30, \quad h=18 C m \\ r &=\frac{30}{2 \pi} \\ r &=4.77 \mathrm{~cm} \end{aligned}
\begin{aligned} \text { Volume } &=\pi r^{2} \times h \\ &=\pi \times 4.77^{2} \times 18 \\ \text { Volume } &=1289.155 \mathrm{~cm} 3 \end{aligned}
When rolled along breadth (18cm)
----------------------------------------------
2 \pi r=18, \quad h=30 \mathrm{~lm}
r=\frac{18}{2 \pi}
r= 2.86 cm
\begin{aligned} \text { Volume } &=\pi r^{2} \times h \\ &=\pi \times 2.86^{2} \times 30 \\ &=773.493 \mathrm{~cm} 3 \end{aligned}
Question 12
Sol :
(i) Given dis of pipe = 7cm = 0.07m
Velocity = 5m\sec
Discharge = Area \times Velocity
=\frac{\pi d^{2}}{4} \times V
=\frac{\pi \times(0.07)^{2}}{4} \times 5
Discharge =0.0192 \mathrm{~m}^{3} / \mathrm{sec}
\begin{aligned} \therefore \text { Discharge } &=19.2 \text { lits } / \text { see } \\ &=19.2 \times 60 \text { lits } / \mathrm{min} \end{aligned}
Discharge = 1154 .53 lits\min
Discharge \approx 1155 \operatorname{lit} / \min
(ii) Dimension of tank = 4 m \times 3 m \times 2.31 m
Discharge =0.0192 m^{3}/sec
1.154 \mathrm{~m}^{3} / \mathrm{min}
Time taken to fill the tank =\frac{\text { Volume of tank }}{\text { Discharge }}
=\frac{4 \times 3 \times 2.31}{1.154}
Time taken to fill the tank = 24min
Question 13
Given
Vessel 1
radius 15cm
Height 40cm
Volume \pi x r^{2} \times h
\pi \times(15)^{2}+40
Volume \quad 28274.33 \mathrm{~cm}^{3}
Vessel 2
Radius 20cm
Height 40cm
Volume \pi x r^{2} \times h
\pi \times(20)^{2}+45
Volume 56548.667 \mathrm{~cm}^{3}
Given
Another vessel with capcity equal to sum of vessel 1 and vessel 2
Let radius of vessel's = R
Height of vessel = 30cm
\left(\pi R^{2}\right) \times 30=28274.33+56548.667
\begin{aligned} 30 \times\left(11 R^{2}\right) &=84823 \\ R^{2} &=\frac{84823}{\pi \times 30} \end{aligned}
R^{2}=900
R=\sqrt{900}
R=30 \mathrm{Cm}
∴ Radius of vessel = 30cm
Question 14
Sol :
Given
Pole height = 7m
Pole diameter = 20cm = 0.2m
Density = 225 \mathrm{~kg} / \mathrm{m}^{3}
Volume of wood = \frac{\pi d^{2}}{4} \times h
=\frac{\pi}{4} \frac{(20)^{2}}{10^{4}} \times 7
Volume of wood =0.219 \mathrm{~m}^{3}
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 = \frac{\pi}{4} d^{2} \times h
=\frac{\pi}{4}(14)^{2} \times 30
Volume of cylinder = 4618.14 \mathrm{cm}^{3}
Volume of wood wasted = Volume of cuboid - Volume of cylinder
= 14 \times 14 \times 30-(4618.14)
Volume of Wood wasted = 1261.85 \mathrm{~cm}^{3}
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