A source producing sound of frequency \(990\) Hz and an observer are initially at rest. If both the source and observer start moving simultaneously towards each other with accelerations \(2\ \mathrm{ms^{-2}}\) and \(4\ \mathrm{ms^{-2}}\) respectively, then the frequency of sound heard by the observer at a time \(t=5\) s is
\[
(\text{Speed of sound in air}=340\ \mathrm{ms^{-1}})
\]
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For Doppler effect when the source and observer move towards each other,
\[
\boxed{
f'
=
f
\left(
\frac{v+v_o}{v-v_s}
\right).
}
\]
If the bodies start from rest with uniform acceleration,
\[
\boxed{v=at.}
\]