Question 519: Waves

Question

A car is moving towards a high  cliff. The driver sounds a horn of frequency $$f$$. The reflected sound heard by the driver has frequency $$2f$$. If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

Accepted Answer

Let f' be the frequency of sound heard by cliff.
$$ 	herefore $$ $$f = {{vf} \over {v - {v_c}}}$$   ...(1)
Now, for the reflected wave, cliff acts as a source,
$$ 	herefore $$ $$2f = {{f'\left( {v + {v_c}} ight)} \over v}$$   ...(2)
$$2f = {{f\left( {v + {v_c}} ight)} \over {v - {v_c}}}$$
$$ \Rightarrow 2v - 2{v_c} = v + {v_c}$$
$$ \Rightarrow {v \over 3} = {v_c}$$

Answer

v/$$\sqrt 2 $$

Answer

v/3

Answer

v/4

Answer

v/2

Waves

A car is moving towards a high cliff. The driver sounds a horn of frequency $f. The reflected sound heard by the driver has frequency 2f$. If v is the velocity of sound, then the velocity of the car, in the same velocity units, will be

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