A careless boy goes to his school with the speed of 4 km/hr. He finds that his school is closed so he comes back to his house with the speed of 6 km/hr.What is his average speed?
The boy travels equal distances with the speed of v1 = 4 kmh-1 and v2 = 6 kmh-1.
The average speed,
vav = 2v1 v2/(v1 + v2)
= (2 x 4 x 6/4+ 6) = 4.8 km/hr.
