Question

a body covers 20 km with 18 km per hour and next 40 km with 36 km per hour find its average velocity

Answer 1

Let the total distance covered by bus be s km

As we know that speed=Distancetimespeed=Distancetime

Which gives, time=Distancespeedtime=Distancespeed

Time for first third is (t) = s320s320

Time for two third is (t′)=2s360(t′)=2s360

Now, we also know that

Averagespeed=TotaldistanceTotaltimeAveragespeed=TotaldistanceTotaltime

Averagespeed=st+t′Averagespeed=st+t′

Putting the values oft,t, &t′t′ from above we get

Averagespeed=ss320+2s360Averagespeed=ss320+2s360

Averagespeed=ss3×20+2s3×60Averagespeed=ss3×20+2s3×60

Averagespeed=ss3×20+2s3×60Averagespeed=ss3×20+2s3×60

Averagespeed=ss60+2s180Averagespeed=ss60+2s180

Averagespeed=s3s+2s180Averagespeed=s3s+2s180

Averagespeed=s5s180Averagespeed=s5s180

Averagespeed=s×1805sAveragespeed=s×1805s

Averagespeed=36Km/h