Question

The centre of mass of a semi-circular ring lies $5\text{cm}$ above the centre of the semi-circle. What is the circumference of the ring?

• A. $20.67\text{cm}$
• B. $27.48\text{cm}$
• C. $24.67\text{cm}$
• D. $18.56\text{cm}$

Answer 1

The correct option is C $24.67\text{cm}$


$Y_{COM}$ of a semi circular ring is at a distance of $\frac{2R}{\pi }$ from the centre.
$\therefore Y_{COM}=\frac{2R}{\pi }=5$
$\Rightarrow R=\frac{5\pi }{2}=7.85\text{cm}$
Circumference of the ring $=\pi R$
$=24.67\text{cm}$