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naveen

· started a discussion

· 1 Months ago

Wrong (Question: 112233.0 )

In the 3rd last step it should be l/1.75-l/1.5=10 hence it question is conceptually wrong as the cyclist was coming from opposite direction and train crosses it (no overtake)

Question:
If a train takes 1.75 sec to cross a telegraph pole and 1.5 sec to a cyclist travelling in opposite direction at 10 m per second, 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, We found a typing error in the explanation...it has been rectified.....Question's language is correct... Keep Learning with Us Best Wishes Team Toprankers
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