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# A train 300 m long crossed a platform 900 m long in 1 minutes 12 seconds. The speed of the train (in km/hr) is A. 40 B. 50 C. 60 D. 70

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A train 300 m long crossed a platform 900 m long in 1 minutes 12 seconds. The speed of the train (in km/hr) is
A. 40
B. 50
C. 60
D. 70
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1. initially the speed of train is 300/72 m/s and it has to cross platform of 900 m so it has to have a speed of 900/72 m/s
so the total speed of train is
300+900/72 m/s
1200/72 m/s
so 1 hr=3600 sec
but already it has taken 72 sec
so t=3600/72=50
muliply and divide by 50
so
1200*50/72*50=60000/3600 m/s
1000m=1km
3600sec=1hr
so

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2. Total Distance = 1200
total time = 72 sec

Speed = D/t
=1200/72
=16.67m/s
SI = 16.67×3600/1000
= 60km/h

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3. 60 km/hr

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(C.) 60km/hr

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5. 300+900=1200
For
1200 m – 72 sec
For
1000m – ?
Cross multiplication
1000×72/1200=60 km/h

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6. Speed = D/T
distance is 300+900=1200m
time is 1 min 12 sec i.e 72sec
speed = 1200/72 m/sec
1200/1000=1.2 distance in km
72/60=1.2, 1.2/60=0.02 time in hours.
speed = d/t
=> 1.2/0.02 (multiply numerator and denominator by 100)
=>120/2
= 60km/hr

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7. Total distance to be coverd by train (300+900=1200m)
Total time taken 72 sec.
So Speed will be= d/t
12*100/72=50/3 m/sec
For Coverting m/sec into km/hr
We need to multiply it by 18/5
I.e. 50*18/3*5= 60km/hr

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8. Time =1 min 12 s=72 s
Distance covered in 72 second =300+900=1200 m
Speed=
time
distance

Speed=(
72
1200

)m/sec=(
3
50

)m/sec=(
3
50

×
5
18

)=60km/hr

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9. Length of train 🚆 = 300 m
Platform length = 900 m
Total Length= 300+900 = 1200m
Speed ⏩ = Distance/Time
Here, Time is 1 minutes 12 seconds. ( 72 seconds)
Speed = 1200/72= 16.6667m/s to convert this into km/hr
For that 16.6667×(18/5) = 60 km/hr

Good time 😊👍

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10. 60km/hr

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11. 60 km/hr

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