posted by lisa
a 4kg box sits, at rest,on the table what is the box's acceleration? b)how much does the box weight? c) what other force acts on the box? how big is this force?
If it is "at rest" that implies it is sitting there not moving therefor not accelerating. Weight is simply mass x gravity (W=mg) where g~9.81(m/s^2). Newtons Second law Net Force = mass x acceleration (F=ma) reveals if the box has a downward force of W, and is not moving, there must be an equal but opposite force to hold it here. The table exerts this force commonly called N. So if F=ma and a is zero n-mg=0 so n=mg.