In which motions are the distance and the displacement the same?

A. A dog chases its tail in a circle four times
B. A bird flies from its nest to the ground and back to its nest.
C. A worm moves 5 cm along a straight crack in a sidewalk.
D. A fish swims all the way across a pond and then halfway back.

A. A dog chases its tail in a circle four times.

Explanation:

Distance can be defined as a scalar quantity. It describes how much area the object covers during its motion. Displacement can be defined as the vector quantity. It refers to the fact that how far an object is from a place. It describes the overall change in the position of the object.

A dog makes a circle four times chasing the tail thus its direction will remain the same.  Its position will remain the same after motion, thus no displacement will occur.  The dog is making a circle on the same place while chasing the tail hence the distance covered will become equal to the net displacement.  

there are mainly three domains in biological classification namely; archaea, bacteria, and eukarya.

archaea includes all the prokaryotic cells which are characterized by their lipid membranes. they have branched hydrocarbon which is attached to glycerol through an ether linkage.

bacteria includes all the prokaryotic cells, the cell membrane of which are made up of the unbranched fatty acid chain. in addition, they are attached to glycerol through an ester bond.

eukarya includes all the eukaryotic cells, that is, the cells contain a nucleus and other membrane-bound cell organelles.

they can be autotrophic as well as heterotrophic, unicellular as well as multicellular

they include kingdoms like protista, plantae, animalia, fungi et cetera.

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