A net force of zero means that all the forces acting on an object are balanced, resulting in no acceleration.
Let's analyze the options:
A. A race car driving around a circular track - Although the car is moving, it is constantly changing direction, which means there is a centripetal force acting on it to keep it moving in a circle. Therefore, this is not experiencing a net force of zero.
B. A pencil sitting on a desk - The pencil is at rest and not moving. The forces acting on it (gravity pulling it down and the normal force from the desk pushing it up) are balanced, so the pencil is experiencing a net force of zero.
C. A rocket launching into space - The rocket is experiencing a net upward force because the thrust from the engines is greater than the downward force of gravity. Hence, it is not experiencing a net force of zero.
D. A person jumping on a trampoline - While jumping, the person is accelerating upwards as they push off the trampoline. During the compression of the trampoline, there are forces involved, so the person is not experiencing a net force of zero.
Based on this analysis, the correct answer is B. A pencil sitting on a desk.