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NEET Sample Paper NEET Sample Test Paper-68

  • question_answer
    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 s. If speed of sound in air is 330 m/s, the speed of engine is                

    A) 10 m/s          

    B) 20 m/s        

    C) 30 m/s         

    D) 40 m/s        

    Correct Answer: C

    Solution :

    If the speed of engine is v, the distance traveled by engine in 5 s will be 5v, and hence the distance traveled by sound in reaching the hill and coming back to the moving driver \[= 900 + \left( 900 - 5\nu  \right) =1800-5\nu \] So the time interval between original sound and its echo \[t=\frac{(1800-5\nu )}{330}\,\,\,=\,\,5\,\,\Rightarrow \,\,\nu =30\,m/s\]


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