Question

A 1g coin is placed on an L.P. record 10 cm from the axis of rotation. The coin is not displaced. The minimum value of coefficient of friction is _____ if rotation speed is 33 1/3 rmp.

• A. 0.09
• B. 0.1
• C. 0.12
• D. None of these

Answer 1

Answer: (C)

0.12

Answer 2

mrω² = μmg

or m = $\frac{0.1 \times \left( \frac{100}{3} \times \frac{2\pi}{60} \right)^{2}}{10} = \frac{\pi^{2}}{81}$