Answer:
A supermassive black hole is a perfectly ordinary black hole that happens to be really, really big.
The answer would be sewage treatment plants
I believe doubling the speed of the marble will increase the kinetic energy when it rolls down a ramp
Sorry if wrong
Answer:
At the beginning you start out with a lot of energy and stamina but as you progress, maybe five minutes in, you start to get out of breath. While breathing harder, you are trying to intake more oxygen and at the 10 minute mark you can feel your muscles burning a little bit and tire out more. At this point you are gasping for oxygen because your muscles are deprived of oxygen and you body makes lactic acids which you muscles can use instead of oxygen. By the end of it you are very tired.
Explanation:
Hope this helps! I am not sure how scientific of an explanation you wanted.
