Desired spacing:

[![enter image description here](https://i.stack.imgur.com/xLQTh.png)](https://i.stack.imgur.com/xLQTh.png)

How can I achieve this?

What I've tried:

```
\documentclass[11pt]{article}
\usepackage{amsfonts,amsmath,amssymb,enumerate}

\begin{document}
\[\vec{v}_f'\]

\[\vec{v}'_f\]
\end{document}

```

Both result in:

[![enter image description here](https://i.stack.imgur.com/JNkON.png)](https://i.stack.imgur.com/JNkON.png)

Thanks.