Question

A car goes from town A to town B with a speed of 30 km/h and returns back
to town A with a speed of 60 km/h. What is the average speed of the car during the complete journey?

Answer 1

A car goes from town A to town B with a speed of 30 km/hr and returns back to town A with a speed of 60 km/hr. So, the displacement by car is 0 km/hr.

{ As it starting and ending points are same. }

Now,

Speed of the car from town A to town B (A→B) = 30 km/hr

Speed of the car from town B to town A (B→A) = 60 km/hr

We have to find the average speed of the car during the complete journey.

Let us assume that the car travels a distance of 'x' km.

Now,

Time = Distance/Speed

In Case 1.

→ Time (t) = x/30 hr.

In Case 2.

→ Time (t') = x/60 hr.

Average Speed is defined as total distance travelled by the total time taken.

Total distance travelled by car = (A→B) + (B←A) = x + x = 2x km

Total time taken by car = t + t'

= x/30 + x/60

= (2x + x)/60

= 3x/60

= x/20

Therefore,

Average Speed = 2x/(x/20)

= (2x × 20)/x

= 40 km/hr

Shortcut Method

S1 = 30 km/hr and S2 = 60 km/hr

Average Speed = (2 × S1 × S2)/(S1 + S2)

= (2 × 30 × 60)/(30 + 60)

= 3600/90

= 40 km/hr

Answer 2

Answer:

hope it will help you dear