Which two issues have increased the need for alternatives to fossil fuels?

Lets say that an object of a certain volume has a certin mass. what happens to its mass when you double its volume?

Explain in physical terms how a microwave oven works. what would happen when you put a conductor in the microwave oven? explain.

You are traveling in a car going at a constant speed of 100km/h down a long, straight highway. you pass another car going in the same direction which is traveling at a constant speed of 80km/h. as measured from your car's reference frame this other car is traveling at −20km/h. what is the acceleration of your car as measured from the other car's reference frame? what is the acceleration of the other car as measured from your car's reference frame?