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(a) At a certain instant, a particle-lik...

(a) At a certain instant, a particle-like object is acted on by a force `vec(F)=(4.0 N) hat(i) - (2.0 N) hat(j) + (9.0 N) hat(k)` while the object's velocity is `vec(v)= -(2.0 m//s) hat(i) + (4.0 m//s) hat(k)`. What is the instan-taneous rate at which the force does work on the object ? (b) At some other time, the velocity consists of only a y component. If the force is unchanged and the instantaneous power is -15 W, what is the velocity of the object ?

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The correct Answer is:
(a) 28 W; (b) `v=7.5` m/s.
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