hiragana questions

Hi, I have been learning hiragana while I'm going through the rocket Japanese course, and have a couple of questions. First of all how come when there is a word with a long o sound instead of writing two o's, they put a u on the end? My second question is how come when chi or shi are voiced they become the same. For example ji,ja,ju, and jo. If someone could explain this to me I would really appreciate it. Japanese is a great language, and I want to make sure that I learn it correctly.

Hi Ryan, the spelling of long sounds "e" and "o" in hiragana is explained in Newsletter Part 22. You are right, when any "o" sound is made long, it is followed by "u". Similarly, when any "e" sound is made long, it is followed by "i". (Of course there are always exceptions!) As for "why" that is, I can only tell you that's how it is when it is written in hiragana. But as for the pronunciation, they are simple long sounds. For your other question, the pronunciation of the voiced sounds of "shi" and "chi" are exactly the same. That's why they are written the same (ji) in romaji. However, when it is spelled in hiragana, some words are spelled with chi with a voiced symbol and some words are spelled with shi with voiced symbol. Unfortunately, you just have to learn them as you learn these words.