Question

a car travels a certain distance with a speed of 50 km/h and returns with a speed of 40km/h .calculate the average speed of the whole journey.

Answer 1

let the car travels a distance x km at 50 km/h. 
=> x/50 hours. 
as car travels the same distance x km at 40 km/h. 
=> x/40 hours. 
Total distance= 2x km 
Total time= x/50 + x/40 hs 
Avg speed = Total dist. / Total time
=> 2x / (x/50 + x/40)  
=> 2 * 50 * 40 / (50 + 40)
=> 44.4 km/h

Answer 2

Answer:

Explanation:

Given :-

Speed in the forward direction, v₁ = 50 km/h

Speed during the return journey, v₂ = 40 km/h

To Calculate :-

Average speed, v(avg) = ??

Formula to be used :-

v(avg) = Total distance/Total time taken

Solution :-

Now, in this case we are neither given the total distance nor the total time taken.

Let us say the distance traveled in the forward direction be x

Total distance, d = x + x = 2x

Time taken during forward journey, t₁ = x/50 h

Time taken during the return journey, t₂ = x/40 h

Total time taken, t = x/50 + x/40 = 9x/200 h

Now,

v(avg) = Total distance/Total time taken

⇒ v(avg) = 2x/9x/200

⇒ v(avg) = 2x × 200/9x

⇒ v(avg) = 400/9

⇒ v(avg) = 44.44 km/h

Hence, the average speed of the whole journey is 44.44 km/h.