Question

For a particle in one dimensional motion, the instantaeous speed is always equal to the magnitude of instantaneous velocity. Why ?

Answer 1

We know that instantaneous speed, ` v_(i) =(ds)/(dt)`.
Wher `(ds)/)dt) =rate of change of distance. The
change of displacement. In one dismensional motion having uniform acceleration, the direction fo velocity dies not chage with time, only the magnitude of velocity changes with time. Therefrom,
` |d vec s| =ds or v_(i) =(ds)/(dt) = |d vec s|/(dt) = |vec v_(i)|.