A) \[i+2j-4k\]
B) \[i-2j-4k\]
C) \[i+2j+4k\]
D) \[i-2j+4k\]
Correct Answer: C
Solution :
[c] Force \[(\vec{F})=2i+j-k\] and its position vector of \[A=2i-j\]. We know that the position vector of a force about origin \[(r)=(2i-j)-(0i+0j+0k)\] or \[r=2i-j\]. Therefore, moment of the force about origin \[=r\times \vec{F}=\left| \begin{matrix} i & j & k \\ 2 & -1 & 0 \\ 2 & 1 & -1 \\ \end{matrix} \right|=i+2j+4k\]
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