Answer:
C. a motorcycle changing speed from 20km/h to 35km/h
Explanation:
The choice not showing unbalanced forces acting on the object is a motorcycle changing speed from 20km/h to 35km/h.
This change in velocity shows that the body is accelerating during the time interval.
When a body is accelerating, it is changing it's motion and this implies that some unbalanced forces are acting in the body. Unbalanced body changes the state of motion of a body from rest to acceleration or deceleration as the case may be.
