A train travelling at a speed of 108 km/hr
and crosses a telegraph post in 24 seconds.
How long will the train take to cross a
bridge
which is a 90
m long?
Answers
Answer:
distance of telegraph please
Step-by-step explanation:
\begin{gathered}\frak Given = \begin{cases} &\sf{The\ speed\ at\ 1st\ journey\ =\ 30km/h.} \\ &\sf{The\ time\ taken\ in\ 1st\ journey\ =\ 20mins\ =\ \dfrac{20}{60}\ =\ \dfrac{1}{3}.} \\ &\sf{The\ speed\ at\ 2nd\ journey\ =\ 50km/h.} \\ &\sf{The\ time\ taken\ in\ 2nd\ journey\ =\ 30mins\ =\ \dfrac{30}{60}\ =\ \dfrac{1}{2}.} \end{cases}\end{gathered}
Given=
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The speed at 1st journey = 30km/h.
The time taken in 1st journey = 20mins =
60
20
=
3
1
.
The speed at 2nd journey = 50km/h.
The time taken in 2nd journey = 30mins =
60
30
=
2
1
.
To find:- We have to find the average speed ?
__________________
\frak{\underline{\underline{\dag As\ we\ know\ that:-}}}
†As we know that:−
\sf{Distance\ travelled\ =\ Speed\ \times\ Time.}Distance travelled = Speed × Time.
\sf{Average\ speed\ =\ \dfrac{Total\ distance}{Total\ time}}Average speed =
Total time
Total distance
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\frak{\underline{\underline{\dag By\ substituting\ the\ values,\ we\ get:-}}}
†By substituting the values, we get:−
\sf \therefore {\underline{Distance\ travelled\ in\ 1st\ journey:-}}∴
Distance travelled in 1st journey:−
\begin{gathered} \sf : \implies {Speed\ \times\ time} \\ \\ \sf : \implies {30\ \times\ \dfrac{1}{3}} \\ \\ \sf : \implies {\purple{\underline{\boxed{\bf 10km.}}}}\bigstar \end{gathered}
:⟹Speed × time
:⟹30 ×
3
1
:⟹
10km.
★
\sf \therefore {\underline{Distance\ travelled\ in\ 2nd\ journey:-}}∴
Distance travelled in 2nd journey:−
\begin{gathered} \sf : \implies {Speed\ \times\ time} \\ \\ \sf : \implies {50\ \times\ \dfrac{1}{2}} \\ \\ \sf : \implies {\purple{\underline{\boxed{\bf 25km.}}}}\bigstar \end{gathered}
:⟹Speed × time
:⟹50 ×
2
1
:⟹
25km.
★
So here:-
Total distance = 10 + 25 = 35km.
Total time = 1/3 + 1/2 = 5/6.
\sf \therefore {\underline{Now,\ finding\ average\ speed:-}}∴
Now, finding average speed:−
\begin{gathered} \sf : \implies {Average\ speed\ =\ \dfrac{Total\ distance}{Total\ time}} \\ \\ \sf : \implies {\dfrac{35}{(5/6)}} \\ \\ \sf : \implies {35\ \times\ \dfrac{6}{5}} \\ \\ \sf : \implies {\purple{\underline{\boxed{\bf 42km/h.}}}}\bigstar \end{gathered}
:⟹Average speed =
Total time
Total distance
:⟹
(5/6)
35
:⟹35 ×
5
6
:⟹
42km/h.
★
Hence:-
\sf \therefore {\underline{The\ average\ speed\ is\ 42km/h.}}∴
The average speed is 42km/h.