Does net force stay the same when a massless pulley is replaced by a pulley with mass

Trumpeter a holds a b-flat note on the trumpet for a long time. person c is running towards the trumpeter at a constant velocity. person b is running away from the trumpeter at the same rate. person d is standing still the whole time. which person hears a frequency that is lower than the b-flat?

What are the phases shown in a and d called?

How to tell if a molecule is polar or nonpolar with electronegativity