Q.4 (iii) Find the number of coins of 2.2 cm diameter and 0.2 cm thick, can be made by melting a metallic right circular cylinder of height 0.2 m and diameter 8.8 cm.
Best answer
Answer: 1600 coins
Height of the cylinder \(= 0.2\) m \(= 20\) cm; its radius \(= \dfrac{8.8}{2} = 4.4\) cm.
Volume of the cylinder \(= \pi r^2 h = \pi (4.4)^2 (20) = 387.2\pi\) cm3.
Each coin is a cylinder of radius \(\dfrac{2.2}{2} = 1.1\) cm and thickness (height) 0.2 cm.
Volume of one coin \(= \pi (1.1)^2 (0.2) = 0.242\pi\) cm3.
Number of coins \(= \dfrac{387.2\pi}{0.242\pi} = \dfrac{387.2}{0.242} = 1600\).
\(\therefore\) 1600 coins can be made.
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