The most important thing in writing almost anything is to consider the intended audience. Who is the intended audience of this paper? Your teacher: it’s for grades and you want it to be good (so, intended audience is especially important). Applied to your question, this means: What topic would your teacher think is a good one? Ask your teacher for topic suggestions, places to begin your work, sample essays, etc.
Another way to brainstorm ideas for a paper is to look at the resources you have to work with. For example, you listed some subjects that interest you (speed,velocity,force,Newton laws,reflection and refraction of the light,mirrors,energy,simple mechanisms,mechanical power,efficiency,mechanical work,elastic force), now choose one and search for information about it in the resources you’re allowed to use (school text? library? internet?). If you don’t find much information, move on to the next subject and search for it. When you find information on a subject, scan through it and see what jumps out at you. Maybe you’ll have a question about something, or you’ll notice something interesting, like a characteristic or pattern – something that will suggest a topic for your paper. If nothing jumps out at you, move onto the next subject search.
If you want this paper to be good, you should ask your teacher for feedback once you settle on a topic. A mistake this early in the game can ruin everything.