Vector Algebra Question 72
Question: A force $ F=2i+j-k $ acts at a point A, whose position vector is $ 2i-j $ . The moment of F about the origin is
Options:
A) $ i+2j-4k $
B) $ i-2j-4k $
C) $ i+2j+4k $
D) $ i-2j+4k $
Show Answer
Answer:
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}= \begin{vmatrix} i & j & k \\ 2 & -1 & 0 \\ 2 & 1 & -1 \\ \end{vmatrix} =i+2j+4k $
BETA
