Please keep all of your questions in one topic (just hit "post reply" when you are already in a topic).
I'm going to merge all of your questions into one topic and move them to the physical science forum, which is more appropriate than math and computer science.
Try searching on "buoyancy" and "density float water" and "height water in a search engine like Google and you should come up with lots of sites to help answer your questions. Once you've done some research on those terms, and if you are still confused about a particular topic, post back to this topic and we can help you. It's your job to do the initial research and do your best to answer your background research questions on your own, but we'll help you AFTER you have tried your best and are still having trouble.
In order to answer your question about dropping an object from a certain height, why don't you make up an experiment and try it out? You could use a clear bucket, a ruler, and a few objects to test it.
Check out our project guide if you are stuck on forming a question, hypothesis, writing your report, or doing analysis: http://www.sciencebuddies.org/science-f ... ndex.shtml
Good luck and let us know if you have any more questions.