Question

Weight of a body would not be zero:
(A). At the center of the earth
(B). During a free fall
(C). In interplanetary space
(D). On a frictionless surface

Answer 1

Hint: The operational definition of weight is the sensation of the gravitational force on a body due to the contact forces that hold it in place. Hence, our weight is essentially the sensation of the normal force from the ground on us when we are standing on it. Thus, if by some means the contact forces vanish, there would be no sensation of the effect of this gravitational force. This condition is known as weightlessness or zero – weight.

Complete step by step answer:

In everyday life, the weight of an object is usually termed as the sensation of the force of gravity acting on its center of mass by the contact forces that try to oppose this force. Hence, the more operational definition of weight is the sensation of the gravitational force on a body due to the contact forces that hold it in place. For example, when a man lifts an LPG cylinder, the weight of the cylinder is felt by the man as the extent of normal force that he has to apply (and hence, by Newton’s third Law, the cylinder applies on him).
If in some situation, the contact forces on the body are removed, there will be no sensation by any contact forces of the gravitational force on it. Hence, it will be termed as having zero weight or being ‘weightless’.
This is the case during free fall. Neglecting air resistance, there are no other contact forces on a body during free fall and hence, its weight is zero.
Also, in interplanetary space, though gravitational force from planets acts on a body. However, there are no contact forces on it and it feels weightless.
However, even on a frictionless surface, a body experiences the normal contact force from the surface which tries to oppose gravity. By the sensation of the normal force, the body is said to have a sensation of weight. Therefore, weight would not be zero on a frictionless surface.
Hence, the correct option is D) on a frictionless surface.

Note: This question can be very confusing since it is not very clear whether to apply the gravitational or the operational definition of weight. The gravitational definition of weight is just the force of gravity acting through the center of mass of a body. This is not zero in free fall or interplanetary space and hence students may be tempted to mark these are the correct options.
However, it is best to use the operational definition for such questions, since it is of a more general and widely accepted nature.