Question 150: Waves

Question

A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is ƒ
1
. If the speed of the train is reduced to 17 m/s, the frequency registered is ƒ
2
. If speed of sound is 340 m/s, then the ratio ƒ
1
/ƒ
2
is -

Accepted Answer

f
app
= f
0
$$\left[ {{{{v_2} \pm {v_0}} \over {{v_2} \pm {v_s}}}} \right]$$
f
1
= f
0
$$\left[ {{{340} \over {340 - 34}}} \right]$$
f
2
= f
0
$$\left[ {{{340} \over {340 - 17}}} \right]$$
$${{{f_1}} \over {{f_2}}} = {{340 - 17} \over {340 - 34}} = {{323} \over {306}} \Rightarrow {{{f_1}} \over {{f_2}}} = {{19} \over {18}}$$

Answer

19/18

Answer

20/19

Answer

21/20

Answer

18/17

Waves

A train moves towards a stationary observer with speed 34 m/s. The train sounds a whistle and its frequency registered by the observer is ƒ 1 . If the speed of the train is reduced to 17 m/s, the frequency registered is ƒ 2 . If speed of sound is 340 m/s, then the ratio ƒ 1 /ƒ 2 is -

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