Chapter 2, Problem 27A

When a box of chocolate bars is in mechanical equilibrium, what can be correctly said about all the forces that act on it? Must the net force necessarily be zero?

To determine

What can be said about all the forces on the chocolate box that is in mechanical equilibrium. And, if the net force on it is necessarily zero.

Answer to Problem 27A

All the forces on the considered chocolate box is balanced, that is equal and opposite. And, yes the net force on that box must be zero if it is in mechanical equilibrium.

Explanation of Solution

Introduction:

An equilibrium is basically a state of no change in the state of the object.

Thus, if the object is in equilibrium, then there will be zero net force on it, that is,

  ${\displaystyle \sum F}=0$

But it does not mean that the forces on it zero, it means that all the forces acting on it are equal and opposite which cancels each other to make the net force zero.

Conclusion:

Hence, the given chocolate box can be in equilibrium even when the forces act on it which are equal and opposite.