Each is grammatically correct. However, "I would be grateful if you could help me with my homework" is eminently more natural and less rude.

Is I would be grateful polite?

In practice, it would be considered very polite. “I would be very grateful for any feedback you can give me on my plan.” This is NOT a conditional sentence, so should not make people feeling like me putting pressure on them.

Would be very grateful meaning?

warmly or deeply appreciative of kindness or benefits received; thankful: I am grateful to you for your help. expressing or actuated by gratitude: a grateful letter. pleasing to the mind or senses; agreeable; welcome: a grateful breeze;The peace and calm of the hill country is a grateful relief.