5 Relative to an origin \(O\), the position vectors of the points \(A\) and \(B\) are given by
$$\overrightarrow { O A } = \left( \begin{array} { r }
- 2
3
1
\end{array} \right) \quad \text { and } \quad \overrightarrow { O B } = \left( \begin{array} { l }
4
1
p
\end{array} \right)$$
- Find the value of \(p\) for which \(\overrightarrow { O A }\) is perpendicular to \(\overrightarrow { O B }\).
- Find the values of \(p\) for which the magnitude of \(\overrightarrow { A B }\) is 7 .