Question

A magnet is in the form of a ring with inner diameter $4cm$ and outer diameter $6cm$. If the thickness of the magnet is $2cm$ . What is the cost of fabricating the surface of the magnet if the cost of fabrication per ${cm}^2$ is $Rs.10$

• A. $Rs.950$
• B. $Rs.945$
• C. $Rs.942$
• D. $Rs.1000$

Answer 1

Answer: (C)

$Rs.942$

Given ,

Inner diameter=4,

inner radius$r_1$=2cm

Similarly outer radius$R_2$=3cm

Thickness t=2cm

Surface area of ring=$2\pi (R^2-r^2)+2\pi (R+r)t$

=$2\pi (3^2-2^2)+2\pi \times 10$

=$30\pi c{m}^2$

Cost of fabricating=Area$\times$Rate

=$30\times 3.14\times 10$

=$Rs942$