year 8 maths

160 Chapter 3 Measurement and Pythagoras’ theorem
Example 18
Finding the volumes of prisms
Find the volumes of these prisms.
a A = 10 cm 2
b
3 cm
2 m
4 m
8 m
SOLUTION
a
V = Ah
= 10 × 3
= 30 cm 3
b V = Ah
1
= ( 2 × 4 × 2 ) × 8
= 32 m 3
EXPLANATION
Write the rule and substitute the given values of A
and h , where A is the area of the cross-section.
The cross-section is a triangle, so use A = 1 bh with
2
base 4 m and height 2 m .
Example 19
Finding the volume of a cylinder
Find the volumes of these cylinders, rounding the answer to two decimal places.
a 2 cm
b
10 cm
14 m
20 m
SOLUTION
a
b
V = πr 2 h
= π × 2 2 × 10
= 125.66 cm 3 (to 2 d.p.)
V = πr 2 h
= π × 7 2 × 20
= 3078.76 m 3 (to 2 d.p.)
EXPLANATION
Write the rule and then substitute the given values for
π , r and h .
Round as required.
The diameter is 14 m so the radius is 7 m .
Round as required.
Cambridge Maths NSW
Stage 4 Year 8 Second edition
ISBN 978-1-108-46627-1 © Palmer et al. 2018
Cambridge University Press
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