Which of these questions can be answered using scientific methods? is history more interesting than algebra? is the color purple more appealing than green? are sundays more hectic than mondays? are the temperatures in your city demonstrating trends in global warming?

The last one, about the trend of the temperatures in my city.

Those can be measured, and described with numbers that mean the same thing to everybody.

On the other hand, "interesting", "appealing", and "hectic" can't be precisely measured, so they can't be studied scientifically.

wavelength divides in half and speed stays the same.

it's when something is going so fast it makes a loud noise, breaking the sound barrier, for example: a jet makes a loud noise, not only cause of the jet but because they reached a point where they went so fast that you can year the noise from various parts, kinda like a police car, lets say the car was going   so fast that you hear the siren of the cop car right next to you, but the car is probably a mile a way, it's cos the siren was next to you a few seconds if you understand me