The purpose of work coordinate systems

1. What G-code designates IPM feed rate mode? IPR feed rate mode?

2. What is the purpose of a clearance plane in CNC programming and milling?

3. What is the purpose of work coordinate systems?

4. Briefly define linear interpolation.

5. If during the last operation on a part, a G1 code command is programmed but no F-value is given in the block, what feed rate will be used?