Question

A boy stops after travelling 3km towards east and then goes 4 km towards north along a plane road.The resultant displacement of the boy is

Answer 1

Since both the displacemnent vectors are mutually perpendicular, the resultant displacement vector's magnitude will be:
$\sqrt{ 3^{2} + 4^{2} } = 5 \ km$

Answer 2

as the boy travelled in a path of 3m and 4m perpendicular to each other thus the displacement made by him is the hypotenuse of the right triangle formed
therefore the displacement made by the boy is 5m