When a car is approaching the observer, the frequency of horn is $100 \mathrm{~Hz}$. After passing the observer, it is $50 \mathrm{~Hz}$. If the observer moves with the car, the frequency will be $\frac{x}{3} \mathrm{~Hz}$ where $x=$ ________________.
Answer (integer)
200
Solution
<p>$100 = {v_0}{v \over {v - {v_c}}}$</p>
<p>$50 = {v_0}{v \over {v + {v_c}}}$</p>
<p>$2 = {{v + {v_c}} \over {v - {v_c}}}$</p>
<p>$2v - 2{v_c} = v + {v_c}$</p>
<p>${v_c} = {v \over 3}$</p>
<p>$$100 = {v_0}{{v \times 3} \over {2v}} \Rightarrow {v_0} = {{200} \over 3} = {x \over 3}$$</p>
<p>$\Rightarrow x = 200$</p>
About this question
Subject: Physics · Chapter: Waves · Topic: Wave Motion and Types
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