Question

a train travels from city A to B with constant speed of 10m/s and returns back to city A with constant speed of 20m/s. Find its average speed during its entire journey

Answer 1

Let the distance between the city A and city B be x ms
Then the total distance travelled is 2x ms
Also, time taken when travelling from city A to city B = x/10 secondsTime taken when travelling from city B to city A = x/20 seconds
Average Speed = Total distance/ Total Time=>                          = $\frac{2x}{ \frac{x}{10} + \frac{x}{20} }$                              = 2/(3/20)                              = 40/3 m/s
This is the Average Speed of the whole journey

Answer 2

Hello Dear.

Here is the answer---

Let the Distance between the Station A and Station B is x m.

In First Case(From A to B).
∵ Time = Distance/Speed
  ⇒Time(T₁) = x/10 seconds.

In Second Case(From B to A).
 Time(T₂) = x/20 seconds.


Total Time(T) = T₁ + T₂
= x/10  + x/20
= (2x + x)/20 seconds.

Total Distance = x + x
  = 2x m.


Using the Formula,
 Average Speed = Total Distance/Total Time
 = 2x/(3x/20)
 = 40/3 m/s.

∴ Average Speed of the Train during the Journey is 40/3 m/s.


Hope it helps.