Answer: External forces are forces caused by external agent outside of the system. Internal forces are forces exchanged by the objects in the system. To determine what part should be considered external and internal, mechanical system should be clearly defined.
Explanation:
The blue ridge would be the answer to your question
Answer: the water will be eroded
Explanation: as the slope of the land becomes steeper, the rate of run-off increases and the water have a better chance or being eroded to a flat land where it can mix with the soil.