Question

When a body is stationary, then:
A) There is no force acting on it.
B) The body is in vacuum.
C) The forces acting on it are not in contact with it.
D) The net forces acting on it balances each other.

Answer 1

Hint: A stationary object is one which is not moving or changing its position. It is at rest. In that position, all the forces acting on it cancel each other’s effect or the sum of the magnitude of all the forces is equal to zero.

Complete answer:
Option A: There is no force acting on it.
When an object is at rest and a force acts on it , the body starts moving in that direction. It changes its position.
When no force acts on the body, it’s velocity will not change and it will be in a static position. Even, when the object is stationary, the force of gravity acts upon it.
Hence option A is not a correct option.

Option B: The body is in vacuum.
Vacuum refers to the space which has no matter. It is entirely free from matter or particles.
Whereas, the body that is at rest or stationary has matter or particles contained in it.
Hence, we can conclude that “when the body is stationary, then the body is not in vacuum”.
Hence, option B is an incorrect option.

Option C: The forces acting on it are not in contact with it.
The above statement is partially correct. Even , when the object is stationary , the forces act on it. But, it is given that they are not in contact with it. The forces acting on the object directly exert their pressure on the body.
Hence, it is not true that the forces acting on it are not in contact with it.
Option C is also an incorrect option.

Option D: The net forces acting on it balances each other.
When a body is stationary , its velocity and also , its acceleration is zero . Several forces act upon it and keep it in static equilibrium. They cancel each other’s magnitude and the sum of magnitude of all the forces acting on it is nullified or made zero.
When the body remains at rest, the resultant or the net external force acting on the body is zero. Hence, when the given body is stationary, the net forces acting on it balance each other.
Hence, Option D is the correct option.
Conclusion :
When the body is stationary , the net forces acting on it balances each other.

Hence, Option D is correct.

Note: Even, when the body is at rest, the gravitational force acts upon it. When the body is stationary, the resultant force acting on it balances each other and it becomes null or zero. Also, the sum of all the forces acting on the body which moves with the constant velocity also balance each other.