Question

What will be the radius of the circle when the cord breaks?

• A. $4.0m$
• B. $1.0m$
• C. $3.0m$
• D. $2.0m$

Answer 1

The correct option is D $2.0m$

Let the radius of the rod when it breaks be $r$.

${\tau }_O=0$, thus angular momentum is conserved about O.

$L_i=L_f⟹m{v}_i{r}_i=mvr$

$4\times 5=vr$

$⟹w{r}^2=20$ (as v=rw) .................(1)

Also, $T=mr{w}^2$

$200=4r{w}^2⟹r{w}^2=50$

From (1), $50=r\times \frac{{20}^2}{r^4}$

$⟹r=2m$