Chapter 7, Problem 50P

(a) At a certain instant, a particle-like object is acted on by aforce $\stackrel{\to }{F}$= (4.0 N) $\hat{i}$ − (2.0 N) $\hat{j}$ + (9.0 N) $\hat{k}$ while the object’s velocity is $\stackrel{\to }{v}$= −(2.0 m/s) $\hat{i}$ + (4.0 m/s) $\hat{k}$. What is the instantaneous 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 −12 W, what is the velocity of the object?