Answer:
[tex]0\; \rm N[/tex].
Explanation:
By Newton's Second Law of motion, the net force on an object is proportional to its acceleration.
The acceleration of an object is the rate of change in its velocity relative to time. On the other hand, the question states that this bookcase is moving at a "constant" velocity. In other words, there is no change in the bookcase's velocity. That means that the rate of change in velocity is zero. Hence, the acceleration of the object is also zero.
By Newton's Second Law of motion, the net force on this object would also be zero.
What about the 160 N of horizontal force? Think about how the floor's normal force on the bookcase balances gravity pull. There is likely another horizontal force (e.g., friction) that balance the 160 N force by acting in the opposite direction. Hence, the overall effect on the bookcase (the net force) would be zero.
In general, whenever an object is moving at constant velocity (in the same direction,) or not moving at all, that object is in a translational equilibrium. The net force on the object would be zero.
