A train travels at a speed of 60 km/hr for 0.52 hr, at 30 km/h for the next 0.24 hr and then, at 70 km/h for the next 0.71 hr. What is the average speed of the train ?
CBSE Class IX Science SA 2 (3 Marks)
Answers
Answered by
107
(i) In the first case, the train travels at a speed of 60 km/h for a time of 0.52 h.
Now, Speed = Distance ÷ Time = 60 km/h
Distance = 60 x 0.52 = 31.2 kin ....(1)
(ii) In the second case, the train travels at a speed of 30 km/h for a time of 0.24 h.
Now, Distance = Distance ÷ Time = 30 km/h
Distance = 30 x 0.24 = 7.2 km .....(2)
(iii) In the third case, the train travels at a speed of 70 km/h for a time of 0.71 h
Now, Speed = Distance ÷ Time = 70 km/h
Distance = 70 x 0.71 = 49.7 km ......(3)
From equation 1, 2 & 3, we get,
Total distance travelled = (31.2 + 7.2 + 49.7) km = 88.1 km
Total time taken = (0.52 + 0.24 + 0.71) h = 1.47 h
Average speed = Total distance travelled ÷ Total time taken
= (88.1 ÷ 1.47)
Hence, average speed
= 59.9 km/h
Now, Speed = Distance ÷ Time = 60 km/h
Distance = 60 x 0.52 = 31.2 kin ....(1)
(ii) In the second case, the train travels at a speed of 30 km/h for a time of 0.24 h.
Now, Distance = Distance ÷ Time = 30 km/h
Distance = 30 x 0.24 = 7.2 km .....(2)
(iii) In the third case, the train travels at a speed of 70 km/h for a time of 0.71 h
Now, Speed = Distance ÷ Time = 70 km/h
Distance = 70 x 0.71 = 49.7 km ......(3)
From equation 1, 2 & 3, we get,
Total distance travelled = (31.2 + 7.2 + 49.7) km = 88.1 km
Total time taken = (0.52 + 0.24 + 0.71) h = 1.47 h
Average speed = Total distance travelled ÷ Total time taken
= (88.1 ÷ 1.47)
Hence, average speed
= 59.9 km/h
Answered by
1
Answer:
59.9 km/h
Explanation:
in this problem, first of all, we have to calculate the distances travelled by train under 3 different conditions of speed and time
1)speed=distance/time
=60=distance/0.52
=60*0.52=distance
=31.2 km
in first case distance of train is 31.2 km (1)
2)speed=distance/time
=30=distance/0.24
=30*0.24=distance
=7.2 km
in second case distance of train is 7.2 km (2)
3)speed=distance/time
=70=distance/0.71
=70*0.71=distance
=49.7 km
in third case distance of train is 49.7 km (3)
from equations 1,2and 3
total distance=31.2+7.2+49.7=88.1 km
total time=0.52+0.24+0.71=1.47 hr
average speed=total distance/total time taken
=88.1/1.47
=59.9 km
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