It’s b all objects with mass experience gravitational attraction I hope this helps
The perceived frequency when the fire truck is moving toward you and away from you will be 370 Hz and 329.59 Hz respectively.
<h3>What is the Doppler effect?</h3>
A sudden change in the frequency due to the distance between the objects and source is explained by the doppler effect.
As the source and observer travel toward each other, the frequency of sound, light, or other waves increases or decreases.
The perceived frequency when the fire truck is moving toward you;

The perceived frequency when the fire truck is moving away from you;

Hence, the perceived frequency when the fire truck in cases 1 and 2 will be 370 Hz and 329.59 Hz.
To learn more about the doppler effect refer to the link;
brainly.com/question/15318474
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Velocity
Because velocity is speed with direction. In this scenario, the speed has not changed, but the direction did.
heat conduction is cut off by vacuum.
metal cover block light thereby protecting radiation