A motorcyclist rides in a horizontal circle about central vertical axis inside a cylindrical chamber of radius 'r'. If the coefficient of friction between the tyres and the inner surface of chamber is ' $\mu$ ', the minimum speed of motorcyclist to prevent him from skidding is $\left({ }^{\prime} \mathrm{g}^{\prime}=\right.$ acceleration due to gravity $)$

• A

  $\sqrt{\frac{\mu g}{r}}$
• B

  $\sqrt{\frac{r \mu}{g}}$
• C

  $\sqrt{\frac{g}{r \mu}}$
• Correct answer
  D

  $\sqrt{\frac{r g}{\mu}}$

Hence, the correct answer is option: 'D'.