The engine of a train moving with speed 10m s ^ - 1 towards a...

The formula to calculate the frequency of the sound as heard by the passenger inside the train can be written as

$f ' = {f}_{0}\left[\dfrac{v - {v}_{O}}{v - {v}_{s}}\right] . . . \left(1\right)$

Since the passenger is inside the train, the speeds of the source and the observer are the same.

Substitute the values of the known parameters into equation (1) to get the required frequency.

$\begin{cases}f ' & = & 400\left[\dfrac{330 - 10}{330 - 10}\right]Hz \\ & = & 400Hz\end{cases}$