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ICSE Class 9 Answered

An engine is approaching a tunnel surmounted by a Cliff and emits a short whistle when 1km away. The echo reaches the engine after 5 second.calculate the speed of engine assuming the velocity of sound to be 340m/s.  
Asked by Palaibabulal838 | 13 Feb, 2019, 10:19: AM
answered-by-expert Expert Answer
Let engine is travelling with speed x m/s.
 
Distance travelled by engine in 5 seconds = 5x m
 
time taken by sound from engine to cliff = (1000/340) s  .................................(1)
 
When echo is reaching the engine, engine has already travelled a distance of 5x.
 
Hencetime taken by echo sound from cliff to engine = [ (1000-5x)/340 ] s ....................(2)
 
since the total time is 5 s, by adding (1) and (2), we get begin mathsize 12px style 1000 over 340 space plus space fraction numerator 1000 minus 5 x over denominator 340 end fraction space equals space 5 space space space space o r space 5 x space equals space 2000 minus 1700 space space space space o r space space space x space equals space 60 end style
hence engine speed is 60 m/s
Answered by Thiyagarajan K | 13 Feb, 2019, 11:02: AM

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