Answer :

Select physics on the ask question drop down menu.
AL2006
-- If you want to ASK a Physics question . . .
Click on the orange block over there  =====>
that says " + Ask a question".
In the new window, there is a drop-down menu where you can
select the category you want your question to go into.

-- If you want to SEE all the Physics questions that other people
have already asked . . .
. . . Click on the orange funnel up at the top, next to the "brainly.com" .
. . . This will open a screen full of all the questions that have been asked
in EVERY category ... all the questions on the site.
. . . At the top of the blue part of the screen, there's a strip that says "All Subjects".
When you click in there, you get a list of categories.  You can click on the one
you're interested in, and the screen changes to only show questions in the
subject you picked.