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?
Answers
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:
hope it will help you dear
