Question

A car travels the first third of the distance with speed 10 kilometre per hour the second third at 20 kilometre per hour and the last third at 60 kilometre per hour what is its means speed over entire distance

Answer 1

Solution:

Let the total distance travelled be 's'.

Hence the time taken for first third of the distance = t1 = s/3 / v1

Similarly, the time taken for second third of the distance = t2 = s/3 / v2

and the time taken for last third of the distance = t3 = s/3 / v3

Hence, the mean speed over the distance = s / t1 + t2 + t3

= 3 / 1/v1 + 1/v2 + 1/v3

= 3 / 1/10 + 1/20 + 1/60 = 18 km/h

Thus, its means speed over entire distance is 18 km/h.