Question

A $1g$ coin is placed on an L.P. record $10cm$ from the axis of rotation. The coin is not displaced. The minimum value of coefficient of friction is $\underset{–}{}$, if rotation speed is $33\frac{1}{3}rpm$.

• A. $0.09$
• B. $0.1$
• C. $0.12$
• D. $0.04$

Answer 1

Answer: (C)

$0.12$

$mr{\omega }^2=\mu mg$ or $\mu =\frac{0.1\times {(\frac{100}{3}\times \frac{2\pi }{60})}^2}{10}$ = $\frac{{\pi }^2}{81}=0.12$