Can you use a half dollar?

Answer 1

Of course! Half dollars are legal circulating coins; they're just not used very often because of problems with their design and composition that happened back in the 1960s. By the time the problems were corrected people had gotten out of the habit of using the denomination.

Note that any half dollar dated 1965 to 1969 is made of 40% silver and is worth more to a collector or metal dealer. However halves dated 1971 and later are only worth face value.