The selection of testing time and sliding velocity for wear testing of Metal Matrix Composite (MMC) material can be determined based on the specific requirements of the experiment, the material properties, and the testing standard being used.

Given that you've specified the sliding distance (500m), load (10N), rotational speed (300 rpm), and track diameter (80mm), you can calculate the sliding velocity and the testing time as follows:

Remember, these calculations are general guidelines. The specific testing conditions might require adjustments based on the nature of the MMC material under investigation and the objective of the wear test. Therefore, always align your experimental setup with the testing standard being followed and the material properties under consideration.

Good luck

Dr Joshua