Complete the following statement. The first condition of equilibrium of a body is :

Sum of all moments on a body should be zero Sum of all force on a body should be zero Sum of the initial and final force should be zero Relative difference of forces should be zero

Sum of all force on a body should be zero

Sum of all the forces on the body : $F_{net}$ We know that, at equilibrium, the potential energy is extremum. Also, $F_{net} = \frac{dU_{net}}{dr} $ As : $\frac{dU_{net}}{dr} = 0 \text{ for extreme U}$ $\Rightarrow F_{net} = 0$