Question

A person travels along the straight road for first half with velocity v1 and second half with velocity v2 find the mean velocity

Answer 1

let the half lengths be x each thus time taken for first length, t1 = x/20time taken for second length, t2 = x/30thus average velocity = 2x/(t1+t2) = 24 m/s

Answer 2

let the half lengths be x each, displacement = S.

Given, he travels first half is x/2 with v1. Displacement = v1 * x/2

Given, he travels second half is x/2 with v2. Displacement = v2 * x/2.

So, S = v1 * x/2 + v2 * x/2 = (x/2)(v1+v2)

  Average velocity = S/x

                               = (x/2)(v1+v2)/x

                              = (v1+v2)/2.


Hope this helps!