Question

a truck moves a distance of 50 km. it covers first half of the distance at speed 200m/s and second half at speed v. if average speed of truck is 100m/s the finf the value of v

Answer 1

Total Distance covered by truck = 50 km

= 50×1000 m = 50000 m

First half is 50000/2 = 250000 km

speed in first half = 200 m/s

time = 25000 / 200 = 125 s

Second half is next 25000 m

speed in second half is v m/s

time = 25000 / v s

So, total time taken in journey

= 125 + 25000/v

= (125v + 25000)/v

As average speed = total distance/total time

and average speed is 100 m /s


so, 100 m/s = 50000/ { (125v + 25000)/v }

or, 100 = 50000v / (125v + 25000)

or, 100 × (125v + 25000) = 50000v

or, 12500v + 2500000 = 50000v

or, 37500v = 2500000

or, v = 2500000 / 37500 = 66.67 m/s

So, v = 66.67 m/s.