Questions

The moment of the force $\mathbf{F}=4\hat{i}+5\hat{j}-6\hat{k}$ acting at (2 0, $-$ 3), about the point (2 $-$2 $-$ 2) is given by

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a

−7i^−8j^−4k^

b

−4i^−j^−8k^

c

−8i^−4j^−7k^

d

−7i^−4j^−8k^

detailed solution

Correct option is D

Moment of force is defined as the cross product of the force and the force arm.Given, F=4i^+5j^−6j^,r1=2i^−2j^−2k^and r2=2i^+0j^−3k^Moment of force =r×F=r2−r1×F=[(2i^+0j^−3k^)−(2i^−2j^−2k^)]×(4i^+5j^−6k^)=(0i^+2j^−k^)×(4i^+5j^−6k^)=i^j^k^02−145−6=i^(−6×2)−(−1×5)]−j^[(−6×0)−(−1×4)]+k^[(0×5)−2×4]=−7i^−4j^−8k^

Similar Questions

A body is placed on a horizontal frictionless surface. When a horizontal force F is applied on the body, it is observed that the body makes only translational motion. The which of the following points may be the positions of its centre of mass?

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