How to detect of an element is over a div?

How to detect of an element is over a div?

Hi, I need to know that when using Jquery Ui  how can you detect if a element is on top of a div  even if  it was dragged onto the div.

I want to display a button that if the element is above a div and when you press this button. It will add it to the div.

Once this element is added to a div. If you right clicked on this element you will get another button that if clicked will take the element out of the div and be ontop of the div in the same location. 

How can one do this? Yes, I have asked something similar in the Jquery UI section but never got a response and it's been over 2 months now.