The frictional torque transmitted in a truncated conical pivot bearing, considering uniform pressure, is

A. $$\frac{1}{2}\mu {\text{Wcosec}}\alpha \left( {{{\text{r}}_{\text{1}}} + {{\text{r}}_{\text{2}}}} \right)$$

B. $$\frac{2}{3}\mu {\text{Wcosec}}\alpha \left( {{{\text{r}}_{\text{1}}} + {{\text{r}}_{\text{2}}}} \right)$$

C. $$\frac{1}{2}\mu {\text{Wcosec}}\alpha \left( {\frac{{{\text{r}}_1^3 - {\text{r}}_2^3}}{{{\text{r}}_1^2 - {\text{r}}_2^2}}} \right)$$

D. $$\frac{2}{3}\mu {\text{Wcosec}}\alpha \left( {\frac{{{\text{r}}_1^3 - {\text{r}}_2^3}}{{{\text{r}}_1^2 - {\text{r}}_2^2}}} \right)$$

Answer: Option D