Is it possible that the physical velocity is constant but the magnitude of the velocity is variable?give an example

yes it is possible

Explanation:

if the body is travelling with uniform speed in a circular track its speed remains the same but the velocity is non-uniform as the direction of the body is changing every time.

eg: a body in uniform circular motion has constant speed but its velocity changes at every point during the course of motion. Whenever, the direction changes, velcoity changes.

muscle endurance

explanation:

i can do 50 in a row ( but i get so tired after that)

waves moving from a fast medium to a slow medium will experience a reflection as light travels more slowly than red light. total internal reflection occurs when the critical angle is.