⦁explain how this scenario is a controlled experiment and identify the manipulated variable.

I am not sure about what the scenario is, but a controlled experiment is only one variable is altered with, this variable is the manipulated variable. The other two variables are the responding and controlled variable. The controlled variable are the variables you keep the same in each experiment. The responding variable is the variable that changes by itself due to the manipulated variable.
For example, you design an experiment to see how a plant growth is affected by the amount of sunlight. To get a reliable answer, you should only change one variable, in this case the amount of sunlight the plant receives. This variable is the manipulated variable.  The controlled variables would be what you keep the same, for example the type of plant, the conditions the plant is faced with, how much water the plant gets and so on. The responding variable is the growth of the plant due to the amount of sunlight the plant receives.

It is increased due to the doppler effect. (apex)