Question

When a body is in equilibrium, its acceleration is
A. Unity
B. Positive
C. Negative
D. Zero

Answer 1

Hint: A body is said to be in equilibrium or in a state of equilibrium is the state when all the forces acting on the body are balanced. When all the forces acting on the body are balanced, the net force acting on the body is zero and hence the acceleration is also zero.

Complete step by step answer:
Force is defined as the push or the pull to a body having some mass, which can change its velocity. We also know that the change in velocity per unit time is known as acceleration. So, if there is a force acting on a body then the body must have some acceleration. Also, mathematically force is equal to mass times the acceleration of a body.
Now, let us discuss about equilibrium state of a body:
A body is always acted upon by many forces, some are calculated and some are ignored during calculations. For example, when we sit on a chair: the gravitational force is acting on our body, also the normal force due to the chair is acting on our body, the Earth is rotating around the Sun so some centripetal force is also acting on our body. But we generally ignore the normal force and the centripetal force due to the same frame of reference. Now, the resultant of all these forces must either increase the mass of our body or provide some acceleration to our body. But this doesn’t happen as the forces are balanced and they all cancel out each other.
So, as our body is not falling into the chair, that means we are in equilibrium state and for resultant force to be zero, the acceleration is zero as our mass is not zero.

So, the correct answer is “Option D”.

Note:
When the net force acting on a body is zero, its acceleration is zero.
Equilibrium is a position where the net forces acting on a body cancels out and results in zero net force.
 Acceleration of a body is also zero when the velocity is moving with a constant velocity.
If there is a force acting on a body then the body must have some acceleration.