I'll probably risk getting banned for this, but I'm taking my chances anyway.
I hate that my brother has a huge temper. He gets angry over the smallest things, mainly at my mother. He would yell at her, tell her to eat a d***, and sometimes hit her. If I intervene, I would make it worse. I believe that he got his temper from our biological father, who was very abusive to our mother. When I pointed it out to him, he didn't care. He's already been arrested twice for his temper and is still taking anger management classes. Unfortunately, they are not helping much, as he still gets angry sometimes. No one will let me call the cops, not even my mom, even though she is the victim of most of this.
I am at a loss at what to do. I can't tell any of my friends this, because they can never trust me the same way again. I hate my brother so much, I sometimes wish that he never existed.

I'm sorry this is happening to you.
Perhaps if you film him doing this and when he is calm show it to him so he can see himself? Sometimes it makes a huge difference to see yourself in contrast to 'living it'. Different perspective.
Also, if he is hitting your mom please do call the police. It is for her safety, your safety and his own good.