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# A Train Travels the First 15 Km at a Uniform Speed of 30 Km/H; the Next 75 Km at a Uniform Speed of 50 Km/H; and the Last 10 Km at a Uniform Speed of 20 Km/H. Calculate the Average Speed for the Entir - CBSE Class 9 - Science

ConceptMeasuring the Rate of Motion - Speed with Direction

#### Question

A train travels the first 15 km at a uniform speed of 30 km/h; the next 75 km at a uniform speed of 50 km/h; and the last 10 km at a uniform speed of 20 km/h. Calculate the average speed for the entire train journey.

#### Solution

(i) In the first case, the train travels at a speed of 30 km/h for a distance of 15 km.
We can find the time as :
"Time" = "Distance travelled"/"Speed"
S0,
t1 = 15/30 hr
= 0.5 hr
(ii) In the second case, the train travels at a speed of 50 km/h for a distance of 75 km.
We can find the time as :
"Time" = "Distance travelled"/"Speed"
So ,

t2 = 75/50 hr
= 1.5 hr
(iii) In the third case, the train travels at a speed of 20 km/h for a distance of 10 km.
We can find the time as :
"Time" = "Distance travelled"/"Speed"
So ,
t3 = 10/20 hr

= 0.5 hr
Total distance covered :
= (15 + 75 + 10) km
= 100 km
Total time taken = (0.5 + 1.5 + 0.5) km
= 2.5
Therefore , Average speed = "Total distance travelled"/"Time"
Now , put the values to get the average speed .
= 100/2.5
= 40 km/hr

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Solution A Train Travels the First 15 Km at a Uniform Speed of 30 Km/H; the Next 75 Km at a Uniform Speed of 50 Km/H; and the Last 10 Km at a Uniform Speed of 20 Km/H. Calculate the Average Speed for the Entir Concept: Measuring the Rate of Motion - Speed with Direction.
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