Question: 120 meter long train
crosses s tunnel of length 80 meters in 20 seconds. Find the time for train to
cross a man standing on a platform of length 130 meters? [Ans. (d) 12 sec]
(a) 24
sec (b) 42 sec. (c) 22 sec
(d) 12 sec (e) None of these
Solution:
Detailed Explanation:
Concept: When a train
crosses an electric pole or a person, it describes a distance equal to its
length. But, when a train crosses a platform or bridge; it describes a distance
equal to the sum of the length of train and platform/bridge.
“When speed is
constant, distance is proportional to the time taken.”
One thing more
(in this question), the train is passing a man, not the platform; so length of
platform doesn’t matter.
First Method: 120
meter long train crosses s tunnel of length 80 meters in 20 seconds, that is, a
distance of 200 meter (120+80) is described in 20 seconds.
Again, since
the train crosses a man standing on a platform of 130 meter (length of platform
does not matter, as the train crosses the man, not the platform); so the train describes
a distance of 120 meter (equal to its length).
200 m ≡ 20 sec
120 m ≡? = 12
sec Ans.
Second Method:
Here, speed is constant, so speed is proportional to the time taken.
T1:T2 = D1:D2
= 200:120 = 5:3
5 ≡ 20 sec, 3
≡? = 12 sec. Ans.
Thk u sir for giving me excellent concept on train.sir plzz send on profit and loss concept and average. Another doubt that when no profit no loss case wht does it mean.I think it means cp=sp
ReplyDeleteA 210m long train takes 6s to cross a man running at 9 kmph in a direction opposite
ReplyDeleteto that of the train. What is the speed of the train? (in kmph)
1) 127
2) 121
3) 117
4) 108
5) 111
what is the process to go about with this.
A 210m long train takes 6s to cross a man running at 9 kmph in a direction opposite
ReplyDeleteto that of the train. What is the speed of the train? (in kmph)
1) 127
2) 121
3) 117
4) 108
5) 111
what is the process to go about with this.