Find the speed (in km/hr) of a 250 m long train if it crosses a 200 m long bridge in 20 seconds.

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Solution

Dear Student,

$L e n g t h o f B r i d g e = 200 m L e n g t h o f t r a i n = 250 m T o t a l d i s \tan c e c o v e r e d b y t h e t r a i n = L e n g t h o f b r i d g e + L e n g t h o f t r a i n T o t a l d i s \tan c e c o v e r e d b y t h e t r a i n = 200 + 250 = 450 m T i m e t a k e n b y t h e t r a i n = 20 s e c o n d s S p e e d = \frac{D i s \tan c e}{T i m e} = \frac{450}{20} = 22.5 m / s W e k n o w, 1 k m = 1000 m \Rightarrow 1 m = \frac{1}{1000} k m \Rightarrow 22.5 m = \frac{22.5}{1000} k m A n d, 1 h o u r = 3600 s e c o n d s \Rightarrow 1 s e c = \frac{1}{3600} h o u r S p e e d = \frac{\frac{22.5}{1000} k m}{\frac{1}{3600} h r} = \frac{22.5}{1000} \times \frac{3600}{1} = 81 k m / h r$

Regards

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