Find the torque by the force, →F=2^i+3^j+5^k acting at the point →r1=5^i+2^j−^k about the point →r2=6^i−4^j+^k.
A
15^i+^j+36^k
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B
36^i+^j−15^k
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C
36^i−15^j+^k
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D
^i+36^j−15^k
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Solution
The correct option is B36^i+^j−15^k
Given, force →F=2^i+3^j+5^k →r=→r1−→r2 =(5^i+2^j−^k)−(6^i−4^j+^k) =−^i+6^j−2^k Torque about point →r2 is given by →τ=→r×→F =(−^i+6^j−2^k)×(2^i+3^j+5^k) =∣∣
∣
∣∣^i^j^k−16−2235∣∣
∣
∣∣ =^i(30+6)−^j(−5+4)+^k(−3−12)