Question

A car moves uphill at 40 km/h and then back downhill at 60 km/h.what is the average speed for the round trip?

Answer 1

Define
d = distance (km) traveled in either direction
t₁ = time (hours) to travel uphill
t₂ = time(hours) to tavel downhill

The time to travel uphill is

`t_(1) = ((d \, km))/((40 \, (km)/(h))) = (d)/(40)\, hours`
Similarly, the time to travel downhill is

`t_(2) = (d)/(60) \, hours`

The total travel time is

`t=t_(1)+t_(2) = (d)/(40) + (d)/(60) = (60d+40d)/(2400) = (d)/(24)\, hours`

The total distance traveled = 2d km

The average speed is

`v= ((2d \, km))/(( (d)/(24) \, h))=48\, (km)/(h)`

Answer: The average speed is 48 km/h