First slide

Vectors

Question

what is the torque of the force F=2i-3j+4k. F acting at the point r=3i+ 2j+3k m about origin.

Easy

A

6i-6j+12k
B

17i-6j-13k
C

-6i+6j-12k
D

-17i+6j+13k

Solution

$\vec{τ} = r \times F = |\begin{matrix} i & j & k \\ 3 & 2 & 3 \\ 2 & - 3 & 4 \end{matrix}|$
=i[2x 4- 3(-3)] +j[3x2-4x3] +k[3(-3)-2x2]
=i17+j(-6) +k(-13)
=17i-6j-13k

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