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An engine approaches a hill with a constant speed. When it is at a distance of 0.9 km, it blows a whistle whose echo is heard by the driver after 5 seconds. If the speed of sound in air is 330 m/s, then the speed of the engine is :A. 80 m/sB. 30 m/sC. 300 m/sD. 360 m/s |
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Answer» Correct Answer - B If the speed of the engine is v the distance covered by engine in 5 sec is 5v The distance travelled by sound in reaching in hill and coming back to the moving driver `= 900 + (900 - 5v)` `= 1800 - 5v` Time interval between original sound and echo is `5 = (1800 - 5v)/(330) :. 1800 - 5v = 1650` `:. v = 30 m//s` |
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