(a) At a certain instant, a particle-like object is acted on by a force F = (3.0 N) - (1.0 N) + (8.0 N) while the object's velocity is v = - (2.0 m/s) + (4.0 m/s) . What is the instantaneous rate at which the force does work on the object?

Question

(a) At a certain instant, a particle-like object is acted on by a force F = (3.0 N)  - (1.0 N)  + (8.0 N)  while the object's velocity is v = - (2.0 m/s)  + (4.0 m/s) . What is the instantaneous rate at which the force does work on the object?
  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