Question

A car covers ha;f of the total distance with speed of 20 kmph and the rest with a speed of 40 kmph.the average speed during journey is(in Kmph)?plz explain it briefly with calculations?

Answer 1

let t1 and t2 be time of journey with speed 20 and 40 respectively
total distance travelled =velocity *time
= 20t1 + 40t2
and 20t1 = 40t2
total time = t1 + t2
now u can calculate avg. speed =total distance /total time
Or
use the formula Vavg=2v1v2/v1+v2
it is obtained by

a vehicle travels half of the distance with speed v1 in time t1and another half with speed v2 in time t2
v1=(L/2)/t1 , v2=(L/2)/t2.......................(1)
Vavg=total distance/total time=(L/2+L/2)/t1+t2=L/t1+t2
substitute t1 and t2 values from (1) in Vavg
Avg speed=2*20*40/20+40
=1600/60
=26.6666 kmph