What's an adequate punishment for a dog who bites?

This dog needs to be properly trained and exercised and not punished in this manner. This dog being on the end of a chain is going to make it more aggressive. Sadly, you being a child cannot go against your parents' wishes no matter how lame that they are. Talk to your parents about rehoming the dog. You do not need a dog with problems. This dog has some dangerous problems like biting in certain circumstances. This can ultimately cause his death. So there are some decisions to be made here for the good of the family and the dog.