Answer:
a) 
b)
Explanation:
Let´s use Doppler effect, in order to calculate the observed frequency by the byciclist. The Doppler effect equation for a general case is given by:

where:





Now let's consider the next cases:




The data provided by the problem is:

The problem don't give us aditional information about the medium, so let's assume the medium is the air, so the speed of sound in air is:

Now, in the first case the observer alone is in motion towards to the source, hence:

Finally, in the second case the observer alone is in motion away from the source, so:

1. Accelarating
2. Constant Speed
3. Decelerating
4. At Rest
5. Accelerating
Hope this helped!
Factor out 8 and then facotr and u get
8/9(9x+1)(9x-1
For the work, applicate formula:

According our data:
W = 12000 N * 1,5 m
W = 18000 J
The work done is <u>18000 Joules.</u>