Question

A particle moves for the first one third of the total time of a journey with a speed 30 km per hour and with speed 15 km per hour for the remaining time average speed during total journey is​

Answer 1

A particle moves for the first one third of the total time of a journey with a speed 30 km per hour and with speed 15 km per hour for the remaining time average speed during total journey is

Let say total journey = J km

One third of J = J/3 km

Speed for J/3 km = 30 km/Hr

Time = Distance/Speed

Time taken for J/3 Km =  (J/3)/30  = J/90 hr

Remaining Distance = J - J/3 = 2J/3

Speed for remaining distance = 15 km/hr

Time taken for remaining distance = (2J/3)/15 - 2J/45 hr

Total time taken for journey = J/90 + 2J/45

= (J/90)(1 + 4)

= 5J/90

=J/18  hr

Total distance = J km

Average speed = J/(J/18) = 18 km/Hr