Question 166: Waves

Question

A train is moving on a straight track with speed $20\,m{s^{ - 1}}.$ It is blowing its whistle at the frequency of $1000$ $Hz$. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound $ = 320\,m{s^{ - 1}}$) close to :

Accepted Answer

${f_1} = f\left[ {{v \over {v - {v_s}}}} ight] = f 	imes {{320} \over {300}}Hz$
${f_2} = f\left[ {{v \over {v + {v_s}}}} ight] = f 	imes {{320} \over {340}}Hz$
$\left( {{{{f_2}} \over {{f_1}}} - 1} ight) 	imes 100 = \left( {{{300} \over {340}} - 1} ight) 	imes 100 = 12\% $

Answer

$18\% $

Answer

$24\% $

Answer

$6\% $

Answer

$12\% $

Waves

A train is moving on a straight track with speed 20\,m{s^{ - 1}}. It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound = 320\,m{s^{ - 1}}) close to :

Choose the correct answer: