Question

A body goes from A to B with a speed of 60km/hr and returns to the starting point with a speed of 40km/hr. Find

(i)Average speed

(ii)Average velocity of the body

Answer 1

Average speed = total distance/total time taken

let the distance be AB, and time taken from A to B be t₁

distance = speed x time

AB = 60t₁

let the distance from B to A be BA and time taken be t₂

so BA = 40t₂

since both the distances are same, so AB = BA

or, 60t₁ = 40t₂

or, 3t₁ = 2t₂

or, t₂= 3t₁/2

So average speed = (AB + BA)/(t₁ + t₂₎

= (60t₁ + 40t₂)/ (t₁ + t₂)

from (1),

average speed = [60t₁ + 40x(3t₁/2)]/[t₁ + (3t₁/2)]

= 48km/hr

Average velocity = displacement/time

= 0/time = 0 (since initial and final positions are same)