The question pertains to the change in frequency of a wave noted by an observer moving in relation to the source, indicating that the concept to invoke is "
Doppler's effect."
The standard formula for the Doppler effect is:

-- (A)
Note that we don’t need to be concerned with the signs here, as all entities are moving toward each other. If something was moving away, a negative sign would apply, but that is not relevant to this scenario.
Where,
g = Speed of sound = 340m/s.

= Velocity of the observer relative to the medium =?.

= Velocity of the source in relation to the medium = 0 m/s.

= Frequency emitted from the source = 400 Hz.

= Frequency recognized by the observer = 408 Hz.
Substituting the given values into equation (A) will yield:


Solving the above will result in,

= 6.8 m/s
The correct result = 6.8m/s
Answer:
The overall length of the spiral, designated as L, is calculated to be 5378.01 m
Explanation:
Provided information:
Inner radius R1=2.5 cm
and outer radius R2= 5.8 cm.
The thickness of the spiral winding is (d) =1.6 \mu m = 1.6x 10^{-6} m
The total length of the spiral can be computed as



= 5378.01 m
Answer:
(A) = 3.57 m
Explanation:
According to the question, the information provided is:
diameter (d) = 3.2 m
mass (m) = 42 kg
angular speed (ω) = 4.27 rad/s
Using the conservation of energy principle, we have
mgh = 0.5 mv² + 0.5Iω²...equation 1
where
Inertia (I) = 0.5mr²
ω = v/r
Revising equation 1, it turns into
mgh = 0.5 mv² + 0.5(0.5mr²)(v/r)²
resulting in gh = 0.5 v² + 0.5(0.5)v²
This simplifies to 4gh = 2v² + v²
thus h = 3v² ÷ 4g... equation 2
Given ω = v/r, we find v = ωr = 4.27 × (3.2 ÷ 2)
which yields v = 6.8 m/s
Next, substituting the value of v into equation 2 gives us
h = 3v² ÷ 4g
h = 3 × (6.8)² ÷ (4 × 9.8)
h = 3.57 m