Question

A car travels up a hill at a constant speed of 40 km/h and returns down the hill at a

constant speed of 60 km/h. Calculate the average speed for the round trip.

Answer 1

let the distance = d
so, total distance = 2d
In first stretch,
distance = d
speed = 40 km/h
time = distance/speed
= d/40 hrs
On second stretch,
distance = d
speed = 60 km/ h
time =distance /speed
= d/60 hrs
total time = d/40 + d / 60
= 3d+ 2d / 120
= 5d/ 120
= d/24
average speed = total distance /total time
= 2d / d / 24
= 2d × 24/d
= 2×24 = 48 km/h