Take an object of mass 7kg on a rough inclined plane angle 30 degrees.
We are told the block remains at rest.
After a bit of resolving you conclude that mu>0.57
Now if you replace the block with a 14kg one? what happens?
Intuitively you would say it is heavier and therefore more likely to slide down the plane??
But in the algebra, Friction is dependent on the mass and so is reaction force so they cancel.
So are we saying the mass does not make a difference to whether an object will slide down a plane?