A source of sound emits sound waves at frequency f_0 . It is moving...

According to Doppler's effect, the apparent frequency of sound when both source and observer are moving towards each other $$\begin{array}{ll} \Rightarrow& f=\frac{\left(v+v_0\right) f_0}{ \left(v-v_0\right)}\\ \Rightarrow & f=\left(\frac{v}{v-v_s}\right)f_0+\left(\frac{v_0}{v-v_s}\right)f_0 \end{array}$$ \Rightarrow \quad f=\left(\frac{f_0}{v-v_s}\right)v_0+\left(\frac{f_0}{v-v_s}\right)v Equation of straight line, $y=m x+c$ which is equation of straight line making an intercept $c$ on $Y$-axis, Slope of the graph =\frac{f_0}{v-v_s} and intercept =\frac{v f_0{ }^{{}^{\circ}}}{v-v_s} This condition is represented in graph A plotted between $f$ and $v_0$. Hence, option (c) is correct.