I am teaching a class and a student asked why "on" changes to "with" in the second sentence.
I need help on my homework.
I'll help you with your homework.
"With" works fine in both sentences, but I feel that "on" doesn't feel natural in the second sentence. I couldn't give a student a grammatical rule about this.
Can anyone explain why "on" doesn't work in the second sentence as in:
I'll help you on your homework.