Answer from cs61c-ap (Nicole Rungsitiyakorn 13543412) for Question 1
With virtual addresses the memory is shared between muliple processes but still provides protection. In the address space each process has the illustion that it has its own private memory with a "fake" address. Phsycal address are the real address in memory and you can translate a "fake" address in the virtual memory to a "real" address in the physical address space. To get a PA from a VA, you need to add the $basewhich is the start of the physical address space.