If the force represented by $3\hat j+2\hat k$ is acting through the point $5\hat i +4\hat j-3\hat k$, then its moment about the point (1, 3, 1) is
Answer & explanation
Correct answer: option 1
We have, $\vec F=3\hat j+2\hat k$.
Let P (5, 4, -3)and O (1, 3, 1) be the given points. Then,
$\vec r=\vec{OP}=4\hat i+\hat j-4\hat k$.
∴ Moment of $\vec F$ about O is given by
$\vec r×\vec F=\begin{vmatrix}\hat i&\hat j&\hat k\\4&1&-4\\0&3&2\end{vmatrix}=14\hat i-8\hat j+12\hat k$.