Chapter 25, Problem 48A

When a driver blows his horn while approaching a stationary listener, the listener hears an increase in the frequency of the horn. Would the listener hear an increase in the frequency of the horn if she were also in a car traveling at the same speed in the same direction as the first driver? Explain.

To determine

Change in the frequency of the sound heard when the listener is moving away with the same speed as the driver blowing horn approaching towards the listener.

Answer to Problem 48A

When the driver and the listener are moving at the same speed in the same direction, then the listener hears no change in the frequency of the horn.

Explanation of Solution

Introduction:According to Doppler Effect, when sound emitted by the source moving towards the listener, heard by listener, then the frequency of the sound increases.

When the first driver moves towards the stationary listener blowing a horn, then she listens louder with the decreasing distance in between. It is because of the Doppler Effect, the frequency of the sound heard by the listener increases.

Now, when the first driver and listener both, move in the same direction at the same speed, then the frequency of the sound remains constant. Since the distance between both source and the observer remain constant.

Conclusion: Thus, there is no increase in the frequency of the sound heard by listener moving away from the source with the same speed at which first driver is moving.