The thing is that the answer key to Round Up 3 says: Watch out! You are going to fall! BUT Be careful or you will burn your hand.
I wonder whether it is possible to interchange 'to be going to do smth' for future simple in the above sentences as the rule goes like this: We use "will" for prediction, warning, offer, promise, threat, polite request, on-the-spot decision, opinion, hope, fear (especially with the words: think, expect, suppose, hope, believe, know, probably, sure etc). e.g.: Be quiet or the teacher will get angry. (warning) I'll write to you every day. (promise)
While we should bear in mind that one of the uses of 'to be going to do smth' is when there's evidence that smth is about to happen: There's going to be rain because the sky is overcast.
So, i can't quite tell one from the other - whether it is a warning or evidence of what is going to happen and could they be applied simultaneously to one case? Meaning, one can use both depending on what they imply.