In a flat collar pivot bearing, the moment due to friction is proportional to

A. $$\frac{{{\text{r}}_1^2 - {\text{r}}_2^2}}{{{{\text{r}}_1} - {{\text{r}}_2}}}$$

B. $$\frac{{{\text{r}}_1^2 - {\text{r}}_2^2}}{{{{\text{r}}_1} + {{\text{r}}_2}}}$$

C. $$\frac{{{\text{r}}_1^3 - {\text{r}}_2^3}}{{{\text{r}}_1^2 - {\text{r}}_2^2}}$$

D. $$\frac{{{\text{r}}_1^3 - {\text{r}}_2^3}}{{{{\text{r}}_1} - {{\text{r}}_2}}}$$

Answer: Option C