Question

An object is said to be in equilibrium when:
1. There is no net force acting on the object.
2. The total clockwise moments about any point is equal to the total anti-clockwise moments about the same point.
3. The object moves with constant velocity
A) 1 only
B) 2 only
C) 1 and 2 only
D) 1, 2 and 3

Answer 1

1. Equilibrium: The state of an object in which all the force acting on the body is balanced is called an equilibrium state, the structural and mechanical state if the system is the same.
2. Translational equilibrium: When there are no net force acts on the body, the body is said to be in translational equilibrium.
3. Rotational equilibrium: When there is no net acceleration on the body, the body is said to be in rotational equilibrium.

Complete step by step solution:
Analyzing the given options:
Option $\left( 1 \right)$ talks about no net force on the object, which means that the object is in translational equilibrium.
Option $\left( 2 \right)$ talks about the moments about any point, the clockwise moment and the anti-clockwise moment are the same, so we can say that the body is in equilibrium.
Option $\left( 3 \right)$ talks about the constant velocity of the body, which means the body has zero acceleration and this does not affect the equilibrium of the body.

Hence the correct option is $\left( {\text{C}} \right)$.

Note:
1. When the center of mass of an object is having constant velocity and at the same time the body is rotating about its center of mass with changing angular velocity.
2. In rotational equilibrium, the torque of the body is zero instead of force.
3. External torque acting in rotational equilibrium is calculated as zero.
4. An object that is rotating in one direction or an object that is not rotating is in a rotating equilibrium.
5. A body that is in a rigid state is said to be in mechanical equilibrium if both linear momentum and non-linear momentum are not changing with time.