Question

1. A car moves a distance of 200 m if cover the first half of distance with 40 km/h and second half with speed v if average speed is 48 km/h find v​

Answer 1

v1 = 30 km/hr = d1/t1 -> d1 = 30t1

v2 = 60 km/hr = d2/t2 -> d2 = 60t2

Since d1 and d2 are each 1/2 the total distance:

d1 = d2 -> 30t1 = 60t2

-> t1 = 2t2

avg v = (total distance)/(total time)

= (d1 + d2)/(t1 + t2)

= (30t1 + 60t2)/(t1 + t2)

= (30(2t2) + 60t2)/(2t2 + t2)

= 120t2/3t2

= 40 km/hr