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JEE · NEET Previous Year Question

$A force F = 5 i + 2 j - 5 k acts on a particle whose position vector is r = i - 2 j + k . What is the torque about the origin?$

Topic: JEE PYQ

Answer: B. Full step-by-step solution below.

A $8 i - 10 j - 8 k$
B $8 i + 10 j + 12 k$
C $10 i - 10 j - k$
D $8 i + 10 j - 12 k$

Correct answer: B

Solution

(b): Here, r = i - 2 j + k F = 5 i + 2 j - 5 k Torque, ı = r \times i = (ij k 1 - 2152 - 5) = i (10 - 2) - j (- 5 - 5) + k (2 - (- 10)) = 8 i + 10 j + 12 k

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