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Vyomdeep

· started a discussion

· 1 Months ago

Either solution or language of question is wrong (Question:637173.0)

You should have mentioned that cyclist is running opposite to train. The solution assumes that cyclist is running in the same direction as train which will give negative speed of train.

Question:
If a train takes 1.75 sec to cross a telegraph post and 1.5 sec to cross a cyclist racing 10 m per second in the opposite direction of the train, then the length of the train is:
Options:
A) 135 m
B) 125 m
C) 115 m
D) 105 m
Solution:
Ans: (d)

Suppose speed of train = x m/s

or length of train = l m

Time taken by trains to cross a telegraph cost 

= \(\cfrac{Length\ of\ train}{Speed\ of\ train }\)

\(\therefore\ 1.75=\cfrac{l}{x}\)

or   \(x=\cfrac{l}{1.75}\)     ........ (i)

\(\therefore\ 1.5=\cfrac{l}{x+10}\)

or  \(x+10=\cfrac{l}{1.5}\) ......... (ii)

Using (i) and (ii)

\(\cfrac{l}{1.75}+10=\cfrac{l}{1.5}\)

or  \(\cfrac{l}{1.5}-\cfrac{l}{1.75}=10\)

or 0.25 l = 10 \(\times\) 1.5 \(\times\) 1.75

 \(\therefore\ \cfrac{10\times1.5\times1.75}{0.25}=105\) m

Knowledge Expert

· commented

· 1 Months ago

Dear student
Given answer is correct. And there is no error in the question.

Regards
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