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Posted by **franck** on Friday, November 2, 2012 at 5:17am.

W

(b) At some other time, the velocity consists of only a j component. If the force is unchanged, and the instantaneous power is -12 W, what is the velocity of the object just then?

m/s jhat

- physics -
**drwls**, Friday, November 2, 2012 at 8:56amBoth questions can be answered using the fact that the rate of doing work (the instantaneous work) is the dot product of V and F vectors.

(a) W = F*V = (4)(-2) + (-3)(0) + (9)(4) = 36 - 8 = 28 W

(b) Let the object's velocity be V*jhat

-12 = F*V = -12

= (-3)(V) = -12

V = 4 m/s, in the j direction

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