Find the torque of a force F = -3i+j+5k acting at the point r = 7i+3j+k. (a) -21i+4j+4k (b) -14i+34j-16k (c) 14i-38j+16k (d) 4i+4j+6k

Answer: (c). τ = r with r = (7,3,1), F = (-3,1,5). τx = 3(5)-1(1) = 14, τy = -[7(5)-1(-3)] = -38, τz = 7(1)-3(-3) = 16 So the answer is (c) 14i-38j+16k.

Find the torque of a force F = -3i+j+5k acting at the point r =… | NEET 1997 (AIPMT)

Q49NEET 1997 · AIPMTEasy

Torque, Couple & Equilibrium of Rigid Bodies

Find the torque of a force $\vec{F} = -3\hat{i}+\hat{j}+5\hat{k}$ acting at the point $\vec{r} = 7\hat{i}+3\hat{j}+\hat{k}$ .

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Answer: (c)

$\vec{\tau} = \vec{r}\times\vec{F}$ with $\vec{r} = (7,3,1)$ , $\vec{F} = (-3,1,5)$ .
$\tau_x = 3(5)-1(1) = 14$ , $\tau_y = -[7(5)-1(-3)] = -38$ , $\tau_z = 7(1)-3(-3) = 16$
So the answer is (c) $14\hat{i}-38\hat{j}+16\hat{k}$ .

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