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A force vecF=(hati+3hatj)N acts on a bod...

A force `vecF=(hati+3hatj)N` acts on a body at a point P, which is at a distance given by `vecr=(3hati+hatj)m` from the axis of rotation.
What is the direction of the torque acting on the body?

A

Positive X axis

B

Positive Y axis

C

Positive Z axis

D

Negative Z axis

Text Solution

Verified by Experts

The correct Answer is:
C

`hatixxhati=hatjxxhatj=0`
`hatixxhatj=hatkand hatjxxhati= - hatk`
Torque `(tau)-vec(r)xxvec(F)`
`=(3hati+hatj)xx(hati+3hatj)`
`=3hatixxhati+3hatjxx3hatjxxhati+hatjxx3hatj`
`=0 + 9 hatk - hat k +0 = 8 hatk`
`:. vectau=8hatk`
`:.` The magnitude of the torque = 8 N - m and the direction of the torque is along the positive direction of the Z axis.
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