As per doppler's Effect of sound we can say when subway is approaching the platform we will have


Similarly we can find the frequency when subway is passing away with same speed from us


now we can find the ratio of two






So the speed of subway is 28.94 m/s
Answer:
3.3619 Nm
54.27472 rad
182.46618 J
86.88 W
Explanation:
= Initial angular momentum = 7.2 kgm²/s
= Final angular momentum = 0.14 kgm²/s
I = Moment of inertia = 0.142 kgm²
t = Time taken
Average torque is given by

Magnitude of the average torque acting on the flywheel is 3.3619 Nm
Angular speed is given by

Angular acceleration is given by

From the equation of rotational motion

The angle the flywheel turns is 54.27472 rad
Work done is given by

Work done on the wheel is 182.46618 J
Power is given by

The magnitude of the average power done on the flywheel is 86.88 W
The process is called Eutrophication, the two main nutrients that cause eutrophication are nitrogen and phosphorus