Is wireless power transfer by induction at 60Hz possible, or does the frequency need to be changed?
It's certainly possible, but AFAIK it usually involves high inductances (beefy coils), high powers (multi-ton induction furnace) or both. I think most consumer-level induction power transfer devices (induction chargers, induction cookers etc) work in the high-kilohertz level, making semiconductor power switching an absolute neccessity, but at the same time many other aspects of the device simpler.