Intrinsic motivation has to do with a personal meaning, a perception of inner value to the person. That is, it comes from the inside out. This new way of motivating is based on autonomy, mastery and purpose.
Based on this, we can conclude that the part of this passage that shows intrinsic motivation is "Mitchell is worried that he has hurt the Phantom Wind" because even though Mitchell is afraid of suffering some punishment he is motivated to return to the barn because worried that the horse is injured.
The rest are things that you need to write down as you do your research: document the source title, the author, the web address, and also any important points that you might find.
