To develop this problem we will apply the concepts related to the Doppler effect. The frequency of sound perceive by observer changes from source emitting the sound. The frequency received by observer 
is more than the frequency emitted by the source. The expression to find the frequency received by the person is,
= Frequency of the source
= Speed of sound
= Speed of source
The velocity of the ambulance is
Replacing at the expression to frequency of observer we have,
Therefore the frequency receive by observer is 878Hz
Answer:
Stroke is the correct answer
The work done on the filled bucket in raising out of the hole is 2, 925 Joules
<h3>How to determine the work done</h3>
Using the formula:
Work done = force * distance
Note that force = mass * acceleration
F = mg + ma
F = 4. 5 * 10 + 28 * 10
F = 45 + 280
F = 325 Newton
Distance = 9m
Substitute into formula
Work done = 325 * 9
Work done = 2, 925 Joules
Therefore, the work done is 2, 925 Joules
Learn more about work done here:
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Acceleration = (change in speed) / (time for the change)
Change in speed = (end speed) - (start speed) = (15 m/s - 7 m/s) = 8 m/s
time for the change = 2 minutes = 120 seconds
Acceleration = (8 m/s) / (120 seconds)
Acceleration = 0.067 m/s²
