Question

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

Answer 1

Hint: A body is said to be stationary, or at rest, when it does not change its position with time. In other words it can be said that the displacement, velocity and acceleration of the body are all zero. Newton’s first law of motion gives the condition for a body to remain at rest.

Complete step by step answer:
When a body is stationary or at rest, it means that it does not change its position with time. According to Newton’s first law of motion, a body continues to remain in the same state of motion or rest until and unless an external unbalanced force acts on it. Therefore, if the body that is at rest has to remain at rest, in the general case, the combination of forces acting on it balances each other out.
As the external forces balance each other out their effect is not felt by the body in the form of any acceleration.
It is not necessary for forces to be in contact with the body to change the state of rest of the body. For example, a magnet can attract an iron coin that is kept nearby at rest and change its state of rest.

Therefore, the correct option is C) The combination of forces acting on it balance each other.

Note:
Whether an object is at rest or not also depends upon the frame of reference that the observer is in. In one frame of reference a body may be at rest with respect to one observer but may be in motion with respect to another observer in a different frame of reference. For example a passenger sitting in a train sees the passenger sitting in front of him to be at rest, but a man standing on the platform will see the man in motion along with the train.