Question

A car travels 30 km at uniform speed of 40 km/h and next 30 km at uniform speed of 20 km/h . Find the average speed .​

Answer 1

Solution:

Given that -

• S1 = 30 km
• S2 = 30 km
• v1 = 40 km/h
• v2 = 20 km/h

We've to find average speed.

Time taken during first interval :

→ Speed = Distance/Time

→ Time = Distance/speed

→ t1 = S1/v1

→ t1 = 30/40

→ t1 = 3/4 h

Time taken during second interval :

→ Speed = Distance/time

→ Time = Distance/speed

→ t2 = S2/v2

→ t2 = 30/20

→ t2 = 3/2 h

Total time = t1 + t2

→ Total time = 3/4 + 3/2

→ Total time = (6 + 3)/4

→ Total time = 9/4

→ Total time = 2.25 h

Now,

Total distance = S1 + S2

→ Total distance = 30 + 30

→ Total distance = 60

We know that,

Average speed = Total distance/Total time

→ Average speed = 60/2.25

→ Average speed = 26.67 km/h

Hence, average speed of car is 26.67 km/h.

Answer 2

Step-by-step explanation:

The total time for the journey is given as,

t= d1/v1+d2/v2

=30/40+30/20

2.25hr

The average speed is given as,

Vavg=d1+d2/t

30+30/2.25

=26.67km/h

Thus, the average speed of the car is 26.67km/h.