A car moving at 108 km h^-1 finds another car in front of it going in the same direction at 72 km h^-1. The first car sounds a horn that has a dominant frequency of 800 Hz. What will be the apparent frequency heard by the driver in the front car? Speed of sound in air 330 m s^-1.

Two trains are travelling towards each other both at a speed of 90 km h^-1. If one of the trains sounds a whistle at 500 Hz, what will be the apparent frequency heard in the other train? Speed of sound in air = 350 m s^-1.

A traffic policeman sounds a whistle to atop a car-driver approaching towards him. The car-driver does not stop and Lakes the plea in court that because of the Doppler shift, the frequency of the whistle reaching him might have gone beyond the audible limit of 20 kHz and he did not hear it. Experiments showed that the whistle emits a sound with frequency close to 16 kHz. Assuming that the claim of the driver is true, how fast was he driving the car’ Take the speed of sound in air to be 330 m s^-1. Is this speed practical with today’s technology?

Two submarines are approaching each other in a calm sea. The first submarine travels at a speed of 36 km h^-1 and the other at 54 km h relative to the water. The first submarine sends a sound signal (sound waves in water are also called sonar) at a frequency of 2000 Hz. (a) At what frequency is this signal received by the second submarine? (b) The signal is reflected from the second submarine. At what frequency is this signal received by the first submarine. Take the speed of the sound wave in water to be 1500 m s^-1.

A small source of sound oscillates in simple harmonic motion with an amplitude of 17 cm. A detector is placed along the line of motion of the source. The source emits a sound of frequency 800 Hz which travels at a speed of 340 m s^-1. If the width of the frequency band detected by the detector is 8 Hz, find the time period of the source.