why does the sound of something moving away from you seem to change to a lower and lower pitch?
a) as the source moves away, the increased distance creates more interference; so the pitch drops.
b) as the source moves away, the frequency of the sound waves is being compressed, so the pitch drops.
c) as the source moves away, the sound waves speed up to reach the observer; this causes the pitch to drop.
d) as the source moves away, the sound waves stretches out relative to the person standing still; so the pitch drops.
eliminate

16. a brave but inadequate rugby player is being pushed backward by an opposing player who is exerting a force of 800 n on him. the mass of the losing player plus equipment is 90.0 kg, and he is accelerating at 1.20m/s2 size 12{1 "." "20"" m/s" rsup { size 8{2} } } {} backward. (a) what is the force of friction between the losing player’s feet and the grass? (b) what force does the winning player exert on the ground to move forward if his mass plus equipment is 110 kg? (c) draw a sketch of the situation showing the system of interest used to solve each part. for this situation, draw a free-body diagram and write the net force equation.