Final answer:
A balanced force situation is exemplified by an asteroid moving at a constant speed through space. Centripetal acceleration is caused by forces such as the tension in a tetherball rope and Earth's gravitational pull on the Moon. A non-constant mass system is represented by a rocket during launch as it consumes fuel.
Step-by-step explanation:
An example of a balanced force could be an asteroid moving at a constant speed through space. This is because when the forces on an object are balanced, they cancel each other out, resulting in no change in the object's motion. A balanced force situation means there is no net force acting on the object, leading to no acceleration according to Newton's first law. Therefore, an object moving at a constant speed (not accelerating) is likely under balanced forces.
Answering the question related to the parachutist, if a gravitational force of 539 N acts on the parachutist and she experiences an air resistance of 615 N after opening her parachute, the forces are not balanced. In fact, she would be slowing down because the air resistance is greater than the gravitational force. However, without the initial velocity of the parachutist, we cannot determine the exact speed without additional information.
In discussing centripetal acceleration, two examples of forces that can cause this type of acceleration are the tension in the rope on a tetherball and the force of Earth's gravity on the Moon. Both of these scenarios involve a continuous force that pulls an object toward the center of its circular path, thus maintaining its circular motion.
Finally, a system whose mass is not constant can be exemplified by a rocket launched from Earth. As the rocket burns its fuel, the mass of the system (rocket plus remaining fuel) decreases over time.