Question

29. Ifmoment of a force F passing through a point with position vector r about origin is given by rx É. Then find the
moment about point whose co-ordinate is (1, 2, 3) of a force represented by 2i +2j+2k acting at the point (-
2,3,1).​

Answer 1

Answer:

A force F=2i+j−k acts at a point A whose position vector is 2i−j. Find the moment of F about the origin If the point of application of F moves from the point A to the point B (position vector 2i+j), find the work done by F.

Medium

ANSWER

r

ˉ

=2i−j

F

ˉ

=2i+j−k

Hence moment of force about origin is

=

F

ˉ

×

r

ˉ

=(2i+j−k)×(2i−j)

=−i−2j−4k

And the work done

=

F

ˉ

.(r

2

−r

1

)

=(2i+j−k).(2i+j−(2i−j))

=(2i+j−k).(2j)

=2 joules