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Plz anyone answer it........

Answer»

To find the torque by the force F= (2i+3j-5k) ACTING on r1= (2i+4j+7k) m about r2= (i+2j+3k) m  

We will find the torque at r1 and subtract it from the torque at r2 as individually they are torques about the origin. USING DETERMINANT METHOD,

τ1 =r1 × F  = i (21+20) + j (-10 -14) + k (8-6) = (41i -24j + 2k)

τ2 = r2 × F=  = i (9+10) + j(-5-6) + k(4-3) = (19i -11j + k)

FINALLY torque about r2 is  

τ2 – τ2 =  19i – 41i -11j+24j +k-2k = (13j -22 I – k)
D)option is right answer.


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