Question : 60 discs each of diameter 21 cm and thickness $\frac{1}{3}$ cm are stacked one above the other to form a right circular cylinder. What is its volume in m3 if $\pi=\frac{22}{7}$?
Option 1: 7.62 × 10–2
Option 2: 8.05 × 10–3
Option 3: 6.93 × 10–3
Option 4: 4.25 × 10–2
Correct Answer: 6.93 × 10 –3
Solution :
Given,
The diameter of the disc = 21 cm
⇒ Radius of the disc, $r$ = $\frac{21}{2}$ cm
Height of 60 discs if they stacked one above the other = 60 × $\frac{1}{3}$ = 20 cm
So, the volume of the cylinder
= $\pi r^2h$
= $\frac{22}{7} × \frac{21}{2} × \frac{21}{2}× 20$
= $6930$ cm
3
As we know,
1 cm
3
= 10
–6
m
So, the volume = 6930 cm
3
= 6.93 × 10
–3
m
3
Hence, the correct answer is 6.93 × 10
–3
m
3
.
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