= (a) At a certain instant, a particle-like object is acted on by a force F = (4.70 N) (2.10 N) + (8.60 N)k while the object's velocity is - (2.30 m/s)i + (3.70 m/s ) 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 -16.0 W, what is the velocity of the object just then? (Give your answer without a unit vector.) (a) Number (b) Number i Units Units