(a) At a certain instant, a particle-like object is acted o a force F = (4.0 N)i – (2.0 x)i + (9.0N)k while the object's velocity is v = – (2.0m/s)i + (4.0m/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 – 12W, what is the velocity of the object?