Question 70

The volume of metallic cylindrical pipe of uniform thickness is 748 c.c. Its length is 14 cm and its external radius is 9 cm. The thickness of the pipe is

Solution

Let internal radius = $$r$$ cm and external radius = $$R=9$$ cm

Length of pipe = $$h=14$$ cm

=> Volume of pipe = $$\pi(R^2-r^2)h=748$$

=> $$\frac{22}{7} \times 14 \times (9^2-r^2)=748$$

=> $$44 \times (81-r^2)=748$$

=> $$81-r^2=\frac{748}{44}$$

=> $$81-r^2=17$$

=> $$r^2=81-17=64$$

=> $$r=\sqrt{64}=8$$ cm

$$\therefore$$ Thickness of pipe = $$9-8=1$$ cm

=> Ans - (C)

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