Answer:
No, the sound produced by screeching brakes is not a useful form of energy, because it does not contribute to stopping the car.
Answer:
a) the three longest wavelengths = 4.8m, 2.4m, 1.6m
b) what is the frequency of the third-longest wavelength = 75Hz
Explanation:
The steps and appropriate formula and substitution is as shown in the attached file.
Look at bitesizes physics section, they have all the information you need to complete this question.
According to Newton`s law. Force exerted by car,

After adding an additional 400 kg of mass, the force will be same therefore the acceleration

Thus, the acceleration after adding the masses is 1.47 \ m/s^2.