A 75 pound box rests on a perfectly smooth horizontal surface. Any horizontal force greater than zero will cause it to start moving. true or false
Since the horizontal surface is perfectly smooth, then there is no way for a frictional force to prevent horizontal motion.
The box is at rest, and so the only force acting on it is the weight pulling it down to the table and the normal force acting against the weight of the box. The box is not falling into the table so the weight (W=mg) equals the normal force.
Elementary physics usually defines the force due to friction as `F=mu N` , where `mu` is the coefficient of friction. Since the surface is perfectly smooth, then `mu=0` .
Any non-zero horizontal force applied to the box will cause it to move.
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