The weight changes but the mass will stay the same.
Wave speed = (wavelength) x (frequency)
= (1.5 m) x (500 / sec)
= 750 m/s .
The way I look at these things is like this:
-- The runner covered 12 meters in 4 seconds.
Average speed = 3 meters per second.
-- Speed at the beginning = zero.
In order to make the average 3, Speed at the end = 6 meters per second.
-- Speed increased from zero to 6 meters per second in 4 seconds.
It must have increased 1.5 meters per second each second.
That's choice-#2.
