Q.

Find the torque about the origin when a force of 3j^N acts on a particle whose position vector is 2k^m.               [2020]
 

1 6i^Nm  
2 6j^Nm  
3 -6i^Nm  
4 6k^Nm  

Ans.

(3)

Here, F=3j^N,     r=2k^m

Torque, τ=r×F=2k^×3j^=-6i^Nm