Question

when is the displacement of a moving body negative? illustrate it

Answer 1

No the distance travelled by a body cant be negative bcz distance is the actual path covered by a body in any time and distance travelled cannot be decrease but displacement can be negative. Diatance is a scalr quantity while displacement is vector quantity. 

Answer 2

Displacement is a vector quantity. it will be negative when the direction is opposite to what you have taken positive