Doppler Effect Questions

The driver of a car travelling with speed $30\text{m/sec}$ towards a hill sounds a horn of frequency $600\text{Hz}$. If the velocity of sound in air is $330\text{m/s}$, the frequency of reflected sound as heard by driver is:

A train moving at $220{\text{ms}}^{-1}$ towards an object emits $1000\text{Hz}$ sound. Some sound reflects back as an echo. The frequency of the echo detected by the driver is: ($v_s=330{\text{ms}}^{-1}$)

A speeding motorcyclist sees traffic jam ahead of him. He slows down to $36\text{km/hour}$. He finds that traffic has eased and a car moving ahead of him at $18\text{km/hour}$ is honking at a frequency of $1392\text{Hz}$. If the speed of sound is $343\text{m/s}$, the frequency of the honk as heard by him will be:

A source of sound $S$ emitting waves of frequency $100\text{Hz}$ and an observer $O$ are located at some distance from each other. The source is moving with a speed of $19.4{\text{ms}}^{-1}$ at an angle of $60^{\circ }$ with the source-observer line. The observer is at rest. The apparent frequency observed by the observer (velocity of sound in air $330{\text{ms}}^{-1}$), is:

A siren emitting a sound of frequency $800\text{Hz}$ moves away from an observer towards a cliff at a speed of $15{\text{ms}}^{-1}$. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is: (Take velocity of sound in air $=330{\text{ms}}^{-1}$)