Question

What is the only case in which magnitude of displacement and displacement are exactly the same?

Answer 1

1)why not travelling backwards?

Displacement is is a vector quantity and distance is a scalar quality.

So if you walk on a line ABC, and you walk from A to C and then walk backwards to B:

Your total displacement will be, AC - CB this is because displacement is a vector and it considers direction.

But

You total distance travelled will be, AC + CB this is because distance is a scalar and it doesn't consider direction.

Now it's clear that why the obeject shouldn't come back for them to be equal.

2)Now, why a straight line?

Look at the following common example:

You can easily understand if the object doesn't follow a straight line its distance is larger than its displacement.