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relative velocity

Two trains each of length 200m and running in parallel track. one overtakes the other in 20 sec and crosses in 10 sec. what are the velocities of trains?
ans: 30m/s and 10m/s
can anyone help me solve this one? i know it should be done using relative velocity. but not so clear.
(edited 10 years ago)
Original post by aachal
Two trains each of length 200m and running in parallel track. one overtakes the other in 20 sec and crosses in 10 sec. what are the velocities of trains?
ans: 30m/s and 10m/s
can anyone help me solve this one? i know it should be done using relative velocity. but not so clear.


I don't think the question is worded perfectly. Although, I'm assuming i do understand what was trying to be said. I'm not great with comprehending questions!


Now, the faster train travels the length of the other train in 10 seconds. Hence, the relative velocity is 200m/10s = 20ms^-1. However, the faster train took 20 seconds to negate the relative displacement. So the initial relative displacement is s*t = 20*20 = 400. So the faster train travelled 400+ 200 m in 20 seconds. This implies it's speed is 600/20 = 30ms^-1. As the relative speed is 20ms^-1, the speed of the slower train is 10ms^-1.

Edit: Forget my rephrasing, it just makes things more confusing. I've removed it now.
(edited 10 years ago)
Reply 2
Avatar for aachal
aachal
OP
Original post by hecandothatfromran
I don't think the question is worded perfectly. Although, I'm assuming i do understand what was trying to be said. I'm not great with comprehending questions!


Now, the faster train travels the length of the other train in 10 seconds. Hence, the relative velocity is 200m/10s = 20ms^-1. However, the faster train took 20 seconds to negate the relative displacement. So the initial relative displacement is s*t = 20*20 = 400. So the faster train travelled 400+ 200 m in 20 seconds. This implies it's speed is 600/20 = 30ms^-1. As the relative speed is 20ms^-1, the speed of the slower train is 10ms^-1.

Edit: Forget my rephrasing, it just makes things more confusing. I've removed it now.

:smile: thank you for the explaination. i was get it now.
Original post by aachal
:smile: thank you for the explaination. i was get it now.


:wink: no problem. May i ask where this undergraduate problem was from?
Reply 4
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aachal
OP
Original post by hecandothatfromran
:wink: no problem. May i ask where this undergraduate problem was from?

oops sorry! it's not an undergrgaduate question. it's from higher secondary level...:tongue:
Original post by aachal
oops sorry! it's not an undergrgaduate question. it's from higher secondary level...:tongue:


yeah, thought so :tongue:.
Reply 6
Avatar for aachal
aachal
OP
Original post by hecandothatfromran
yeah, thought so :tongue:.

and if you dont mind can i ask you another question related to relative velocity?:colondollar:
Original post by aachal
and if you dont mind can i ask you another question related to relative velocity?:colondollar:



You don't need to ask if you can ask.
Just ask. :smile:
This is an open forum and anyone can respond to your question if they know the answer.

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