Systems of Particles and Rotational Motion — Physics STD 11 Science — Question

1. $\frac{\text{mv}^2}{\text{r}}\times\pi\text{r}$
   
2. $\text{Zero}$
   
3. $\frac{\text{mv}^2}{\text{r}^2}$
   
4. $\frac{\pi\text{r}^2}{\text{mv}^2}$
   

$\text{U}(\overrightarrow{\text{r}_2})-\text{U}(\overrightarrow{\text{r}_1})=-\int\limits^{\vec{\text{r}}_2}_{\vec{\text{r}_1}} \vec{\text{B}}.\text{d}\vec{\text{l}}.$

Apply this equation to a closed curve enclosing a long atraicht wire. The RHS of the above equation is then $-{\mu}_\text{o} \text{ i}$ by Ampere's law. We see that $\text{U}(\vec{\text{r}_2})\neq\text{U}(\vec{\text{r}_1})$ even when $\vec{\text{r}_2}=\vec{\text{r}_1}.$Can we have a magnetic acalar potential in this case?