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Question

Physics Question on work, energy and power

Find the torque about the origin when a force of 3 j^ N3 \,\hat{j}\, N acts on a particle whose position vector is 2 k^ m2\, \hat {k}\, m .

A

6i^ Nm6 \hat{i}\, Nm

B

6j^ Nm6 \hat{j} \,Nm

C

−6i^ Nm-6 \hat{i} \,Nm

D

6k^Nm6 \hat{k} Nm

Answer

−6i^ Nm-6 \hat{i} \,Nm

Explanation

Solution

Given: F⃗=3j^ N\vec{F}=3 \hat{j}\,N,
r⃗=2k^\vec{r}=2\hat{k}
We know, τ⃗=r⃗×F⃗=2k^×3j^\vec{\tau}=\vec{r}\times\vec{F}=2\hat{k}\times3\hat{j}
=6(k^×j^)=6(−i^)=6\left(\hat{k} \times\hat{j}\right)=6\left(-\hat{i}\right)
τ⃗=−6i^ Nm\vec{\tau}=-6 \hat{i}\,Nm