Find the torque due to three forces (in Nm) ^i+3^j−2^k, 4^i+2^j−3^k and −^i+^j−5^k acting on a particle at a point P(3,1,2) about the point A(2,−1,0).
A
−2^i−32^j−14^kNm
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B
−32^i+18^j−2^kNm
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C
32^i+2^j+14^kNm
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D
−32^i+2^j−14^kNm
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Solution
The correct option is B−32^i+18^j−2^kNm Resultant force →F=(^i+3^j−2^k)+(4^i+2^j−3^k)+(−^i+^j−5^k) →F=4^i+6^j−10^kN →r=AP=^i+2^j+2^k
Thus, torque of resultant force about A is →τ=→r×→F=∣∣
∣
∣∣^i^j^k12246−10∣∣
∣
∣∣=−32^i+18^j−2^kNm