if a body is at rest,the net external force acting on it cannot be zero.Is it correct?
Answers
Answer:
yes if if body is in rest then a net external force acting on it will be zero the only force considered will be gravitational force but it can be excluded for practical experimental purpose show in general is a body is in rest there is no external force acting on it.
Answer:
Explanation: Lets try to understand this conversely. If a body is in rest, and we assume its in inertial frame of reference (where Newton’s laws are applicable), then there is one force that will definitely act on it is acceleration due to gravity. But then Physics is weird since we can assume that some how this body is in Newtonian Physics and not under Earth’s or any other Body’s Gravitational Force. In that case, no net force acting on it can mean body is either in a stable equilibrium or net external forces (which could be sum of internal forces too) acting on the body cancel out. Such forces are said to be conservative forces and work done is zero. So now we say, body is in rest with no net external forces acting on it, the forces being conservative and work done is zero, hence.
Now hitting at your question, take the converse of it. If the body is not in rest position, definitely there has been some external force which set it into motion. This external force cannot be zero.
Thus, the statement is true!