Question

A disc rotates with constant frequency of $60rpm$. The maximum distance from the centre of the disc, where a coin can be placed before it filled off, is (The coefficient of friction is $0.4$ and $g=10m/s^2$)

• A. $1/{\pi }^{2}metre$
• B. $1/\pi metre$
• C. ${\pi }^{2}metre$
• D. $\pi metre$

Answer 1

Answer: (A)

$1/{\pi }^{2}metre$

$W=\frac{2\pi }{T}$

or, $66rpm=\frac{2\pi }{T}$

or, $T=\frac{2\pi }{60}=\frac{\pi }{30}$

distance $=\frac{30}{\pi }\times \frac{4}{100}\times \frac{20}{\pi }=\frac{1}{{\pi }^2}m$