JEE Main & Advanced Sample Paper JEE Main Sample Paper-43

  • question_answer
    A person feels 2.5% difference of frequency of a motorcar horn. If the motorcar is moving to the person and the velocity of sound is 320 m/s, then the velocity of car will be

    A)  8 m/s (approx)           

    B)  800 m/s          

    C)  7 m/s             

    D)  6 m/s (approx)

    Correct Answer: A

    Solution :

     By Doppler's formula \[\phi '\] \[\tan \,\phi =\frac{V}{{{H}^{.}}}=\frac{V}{H\,\cos \,\theta }\]  \[\frac{\tan \,\phi '}{\tan \,\phi }=\frac{V/H\,\cos \,\theta }{\frac{V}{H}}=\frac{1}{\cos \,\theta }\] Now adding 1 to both the sides. \[{{\phi }_{1}}=\] \[=BA\] or         \[{{\phi }_{2}}=\] or \[||\]

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