question_answer

Let \[\hat{u}\] and \[\hat{v}\]  be unit vectors such that \[\hat{u}.\,\hat{v}=0.\] If \[\overrightarrow{r}\] is any vector coplanar with \[\hat{u}\] and \[\hat{v}\], then the magnitude of the vector \[\overrightarrow{r}\times \left( \hat{u}\times \hat{v} \right)\]  is _____.

A)  \[|\overrightarrow{r}|\]    

B)  \[2|\overrightarrow{r}|\]

C)  1                                

D)  0

E)  None of these