If F = (60i + 15j - 3k) N and v = (2i - 4j + 5k) m/s, then instantaneous power is (a) 195 watt (b) 45 watt (c) 75 watt (d) 100 watt.

Answer: (b). P = F · v. P = (60)(2) + (15)(-4) + (-3)(5) = 120 - 60 - 15 = 45 W So the answer is (b) 45 watt.

If F = (60i + 15j - 3k) N and v = (2i - 4j + 5k) m/s, then… | NEET 2000 (AIPMT)

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Power

If $\vec{F} = \left(60\hat{i} + 15\hat{j} - 3\hat{k}\right)$ N and $\vec{v} = \left(2\hat{i} - 4\hat{j} + 5\hat{k}\right)$ m/s, then instantaneous power is

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Answer: (b)

$P = \vec{F} \cdot \vec{v}$ .
$P = (60)(2) + (15)(-4) + (-3)(5) = 120 - 60 - 15 = 45\text{ W}$
So the answer is (b) 45 watt.

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