Very often you must have seen traffic police stopping motorists or scooter drivers who drive fast and fine them. Does fine for speeding depend on average speed or instantaneous speed? Explain.

A traffic policeman sounds a whistle to stop a car-driver approaching towards him. The car-driver does not stop and takes 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 ?

The driver of a car travelling at 72 kmph observes the light 300 m ahead of him turning red. The traffic light is timed to remain red for 20 s before it turns green . If the motorist wisher to pass the light without stopping to wait for it t turn green , determine . The speed with which the motorist crosses the traffic light .

On a 60 km straight road, a bus travels the first 30km with a uniform speed of 30kmh^(-1) . How fast must the bus travel the next 30 km so as to have average speed of 40kmh^(-1) for the entire tirp?