Question

a car travels first 30 km with a uniform speed of 20 km/hr and next 30 km at a uniform speed of 40 km/h. What is its average speed.​

Answer 1

Total distance = 30 + 30 = 60 km

Time taken for first journey, t1 = Distance / Speed

==> t1 = 30 / 20

==> t1 = 3/2 h

Time taken for second journey, t2 = Distance / Speed

==> t2 = 30 / 40

==> t2 = 3/4

Total time taken, T = t1 + t2

==> T = 3/2 + 3/4

==> T = 6 + 3/4

==> T = 9/4 h

Average Speed = Total Distance / Total Time Taken

==> Avg. speed = 60 / (9/4)

==> Avg. speed = 60×4 / 9

==> Avg. speed = 80/3

==> Avg. speed = 26.66 Km/h

Answer 2

average speed =Total distance /total time

t1=30/20=1.5s

t2=30/40=0.75s

therefore total distance=60km

=60/1.5+0.75

=60/2.25

8/3km/h=2.6666