The edge of a cutting hand instrument is rested on a dental tray, which causes it to slide. What does this determine?
Sharpness Test:

It is a method of testing the sharpness. Sharpness of an instrument can be tested by lightly resting the cutting edge on a hard plastic surface.  
If the cutting edge digs in during an attempt to slide the instrument forward over the surface, the instrument is sharp. 
If it slides, the instrument is dull. Only very light pressure is exerted in testing for sharpness.

Ref: Sturdevant's art and science of operative dentistry. 4th edition page 321
The instrument is unbalanced
The instrument is dull
The instrument is very heavy
The instrument needs to be replaced