Answer:
Step-by-step explanation:
I'm assuming these are personal questions? Because a few of your questions are incorrect. I'll do my best to explain the ones I do know.
1.) Nobody actually knows what would happen if you travel faster than light. Einstein showed this was impossible due to it requiring an "infinite" amount of energy. My personal belief is that time itself stops existing. Your guess is as good as mine, nobody really knows.
2.) Most objects in the universe are round mostly because of gravity and density. All objects in the universe strive for minimum energy states. A sphere has a minimum gravitational potential than other geometry.
3.) Again, this is another one where nobody knows "why." On the macroscopic, there is classical mechanics. Then once you go into the microscopic world, you enter the realm of quantum mechanics. It's not that the "laws" are different. There is still conservation of momentum and such. Its just that they're expressed differently.
4.) The explanation for this is most likely due to light being composed of particles, photons. Sound cant travel if there is no medium, because sound is purely a wave. There is no such thing as a sound particle, at least not a physical one. You can think of light as traveling photons carrying energy. That's the particle interpretation of light.
Space missions do not use the Earth's momentum to catapult things in space. Each mass in the universe creates a corresponding gravitational field. So, planets create gravitational fields. The current theory of gravity is Einstein's theory of General Relativity, which states that energy and momentum curve spacetime. Special relativity proved the energy/mass equivalence. General relativity predicts that spacetime will curve around large masses. You can think of planets bending spacetime like a bowling ball in the center of a trampoline. This process in reality is 3-D and not 2-D like the trampoline analogy. But, the entire process of "catapulting" is using these gravitational "wells" of spacetime to minimize fuel and travel time.
5.) We don't know what beyond the observable universe. From the Big Bang, the universe only existed for about 13 billion years. So, light only traveled for 13 billion years long. We cant see passed the observable universe if the light hasn't even reached us yet. The reason the size of the observable universe is larger than 13 billion light years, is because we predict the universe is expanding faster than the speed of light. Special relativity demands that mass cannot go faster than the light, but it never restricted spacetime itself.
6.) Planets use gravity to keep their atmosphere. We could theoretically place a massive object on a planet and increase the gravitational field. But that is really impractical. We can't "create" gravity because we dont know if gravity is a particle. We only think of it at the moment as a non-physical wave, a ripple in spacetime. I have personal thought experiments in how we could terraform a planet, and create atmospheres. But that goes into electromagnetism, and not gravity.