Use formula for Echo which is Velocity=2(Distance)/time so 343=2(150)/T 343T=300..T=300/343=0.9 seconds
C.<span>a stable internal attribution</span>
Frequency is defined as the number of repetitions of waves occurring in 1 second. The frequency heard by the man as the ambulance move toward him will be greater than 450 Hz.
<h3>
What is the frequency ?</h3>
Frequency is defined as the number of cycles completed in 1 second. Frequency is given by the formula as,

As the formula shows frequency is inversely proportional to the time that shows if the time is decreasing frequency will increase and vice versa.
In the above case, the ambulance is moving toward the men. So that the time to meet up is decreased that's why the frequency will be greater than the initial frequency from the siren.
Hence the frequency heard by the man as the ambulance move toward him will be greater than 450 Hz.
To learn more about frequency refer to the link ;
brainly.com/question/4393505
B. How many people were included in the study.
During the time that the pencil is exerting 50N of force on the marble, the marble is exerting 50N of force in exactly the opposite direction on the pencil. <em>(D) </em>The mass of the marble doesn't matter, and it doesn't even matter whether the marble is moving or perfectly still.
As soon as the pencil stops exerting any force on the marble, the marble immediately stops exerting any force on the pencil.