Question

A train running at a uniform speed passes a bridge 300 m long in 15 seconds and another bridge 450 m long in 21 second .Find the trains apeed​

Answer 1

length of the bridge (L 1) =300 m

time taken(t 1) =15 sec

total distance covered by the train

= length of the bridge + length of the train

=300 + L

Let, the length of the train be L

total distance covered by the train=300+L

we know that ,

$\bigstar\boxed{\mathtt{speed =\frac{distance }{time } }}$

Now substituting the given values in the above equation we get ,

$\rightarrow\mathtt{speed =\dfrac{300+L }{15 } }..(1)$

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length of the bridge (L 2) =450 m

time taken(t 2) =21 sec

total distance covered by the train

= length of the bridge + length of the train

=450 + L

Let, the length of the train be L

total distance covered by the train=450+L

we know that ,

$\bigstar\boxed{\mathtt{speed =\frac{distance }{time } }}$

Now substituting the given values in the above equation we get ,

$\rightarrow \mathtt{speed =\dfrac{450+L }{21 } }...(2)$

Now equating equations (1) and (2) we get

$\rightarrow\mathtt{\dfrac{300+L }{15 } }=\mathtt{\dfrac{450+L }{21 } }$

$\rightarrow\mathtt{300\times21+21L} }=\mathtt{450\times 15 +15L}$

$\rightarrow\mathtt{6300+21L} }=\mathtt{6750 +15L}$

$\rightarrow\mathtt{21L-15L} =\mathtt{6750 +6300}$

$\rightarrow\mathtt{6L} =\mathtt{450}$

$\rightarrow\mathtt{L} =\mathtt{75m}$

length of the train = 75 m

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Substituting the value of L in equation(1) we get ,

$\rightarrow\mathtt{speed =\dfrac{300+75 }{15 } }$

$\rightarrow\mathtt{speed =\dfrac{375}{15 } }$

$\rightarrow\boxed{\mathtt{speed =25\dfrac{m}{s} }}$

The speed of the train is 25 m/s

Answer 2

Answer:

length of the bridge (L 1) =300 m

time taken(t 1) =15 sec

total distance covered by the train

= length of the bridge + length of the train

=300 + L

Let, the length of the train be L

total distance covered by the train=300+L

we know that ,

Now substituting the given values in the above equation

length of the bridge (L 2) =450 m

time taken(t 2) =21 sec

total distance covered by the train

= length of the bridge + length of the train

=450 + L

Let, the length of the train be L

total distance covered by the train=450+L

we know that ,

Now substituting the given values in the above equation we get ,

Now equating equations (1) and (2) we get

length of the train = 75 m

Substituting the value of L in equation(1) we get ,

The speed of the train is 25 m/s

Step-by-step explanation:

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