Consider you are standing well off to one side of a straight road and the ambulance coming along the road at constant speed, the frequency that you hear decreases all the time as the ambulance approaches and goes past you. How rapidly it changes. At which stage of the motion is the rate of decrease of the frequency greatest?
Consider you are standing well off to one side of a straight road and the ambulance coming along the road at constant speed, the frequency that you hear decreases all the time as the ambulance approaches and goes past you. How rapidly it changes. At which stage of the motion is the rate of decrease of the frequency greatest?
The correct option is C A little after the ambulance has come closest to you.
The rate of decrease in frequency will be greatest when the component of the ambulance's velocity in the direction towards you changes most rapidly. That occurs when the line from the horn to you is perpendicular to the motion (the point of closest approach). The most rapidly changing sound is emitted when the ambulance is closest, but by the time the sound gets to you the ambulance will have moved on a little, so C is a better answer than B.
The rate of decrease in frequency will be greatest when the component of the ambulance's velocity in the direction towards you changes most rapidly. That occurs when the line from the horn to you is perpendicular to the motion (the point of closest approach). The most rapidly changing sound is emitted when the ambulance is closest, but by the time the sound gets to you the ambulance will have moved on a little, so C is a better answer than B.
