Originally Posted by topsquark

What have you been able to do with them?

For example, the first and second problems deal with circular motion with a constant speed. So it's a good bet that the centripetal force will come into play. In this case there is only one force on Uranus (gravity) so that must be the net force. Thus
[LaTeX Error: Can't write to directory]

[LaTeX Error: Can't write to directory]

Which leads to
[LaTeX Error: Can't write to directory]

Now that you have [LaTeX Error: Can't write to directory] the rest is simple. Just find T:
[LaTeX Error: Can't write to directory]

Try that on problem 2 and let us know where you are with the other problems.

-Dan