Answer
(c) its free-body diagram
Work Step by Step
The observer is at rest in his frame and for him the object is moving in the opposite direction.
So the velocity of the object measured by the observer will not be correct.
Since kinetic energy is function of velocity, its measurement also will not be correct.
The free-body diagram shows only the forces acting on the object. So it is same in both frames, the frame of object and the frame of the observer.
