Question: Physics package and multiplication

I have a very simple task:


the result is of course a*b.  However if I load the Physics package beforehand, that is,


the followinkg error shows up:

Error, unrecognized conversion: Physics:-`*`

I have read that the Physcs package redefines the mutiplication. This must be the source of the problem.
But how can I proceed. I need to do this task with the Physics package loaded. 
Any help will be appreciated! 

Please Wait...