9. a train travels 20 km at a uniform speed of 60 km/h and the next 20 km at a uniform speed of 80 km/h. calculate its average speed
A)68.57 km/h
B)70 km/h
C)65.78 km/h
D)72.36 km/h
Answers
Answered by
2
ANSWER :
68.57 Km/h
EXPLANATION :
for 1st
D =20km
S=60km/h
T= D/S
T= 20km/60km/h
t=1/3h
again
t= 20km/80km/h
t= 1/4h
now averagespeed =40/7/12 =68.57 km/s
Answered by
0
Answer:
Explanation:
First case:
Distance=20km
=20×1000
=20000m
Speed=60km/hr
=60×1000/3600
=50/3m/s
Total time =distance/speed
=20000×3/50
=1200s
2nd case:
Distance =20km=20000m
Speed =80km/hr
=200/9m/s
Time taken =20000×9/200=900s
Therefore,
Average speed =Total distance/total time
=(400000/2100)m/s
=19.0476190476m/s
=19m/s
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