Q.
A force of- F $\widehat{\mathbf{k}}$ acts on $O$, the origin of the coordinate system. The torque about the point (1, -1) is
A) $F\left( \widehat{\mathbf{i}} - \ \widehat{\mathbf{j}} \right)$
B) $- F\left( \widehat{\mathbf{i}} + \ \widehat{\mathbf{j}} \right)$
C) $F\left( \widehat{\mathbf{i}} + \widehat{\mathbf{j}} \right)$
D) $- F\left( \widehat{\mathbf{i}} - \ \widehat{\mathbf{j}} \right)$
Explanation
(c) [image:7_image129.emf]
$\tau = \mathbf{r} \times \mathbf{F}$
$\tau = \left( \widehat{\mathbf{i}} - \widehat{\mathbf{j}} \right) \times ( - F\ \widehat{\mathbf{k}})$
$= F\lbrack\left( - \widehat{\mathbf{i}} \times \widehat{\mathbf{k}} \right) + \left( \widehat{\mathbf{j}} \times \widehat{\mathbf{k}} \right)\rbrack$
$= F\lbrack\widehat{\mathbf{i}} + \widehat{\mathbf{j}}\rbrack$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.