Question

A coin placed on a gramophone record rotating at $33rpm$ flies off the record, if it is placed at a distance of more than $16cm$ from the axis of rotation. If the record is revolving at $66rpm$, the coin will fly off if it is placed at a distance not less than

• A. $1cm$
• B. $2cm$
• C. $3cm$
• D. $4cm$

Answer 1

The correct option is D $4cm$

$\mu mg=mr4{\pi }^2{v}^2$
$\Rightarrow r_2{v}_2^2=r_1{v}_1^2\Rightarrow r_2=\frac{r_1{v}_1^2}{v_2^2}=\frac{r_1{v}_1^2}{4v_1^2}$
$r_2=\frac{r_1}{4}=4cm$