The Doppler effect is the right concept to solve this problem. The Doppler effect is understood as the change in apparent frequency of a wave produced by the relative movement of the source with respect to its observer. Mathematically it can be described as,
Here,
= Frequency of the sound from the Whistle
f = Frequency of sound heard
v = Speed of the sound in the Air
Replacing we have that
Therefore the minimum speed to know if the whistle is working is 16.33m/s
Answer:
<em>1108.464 N of force</em>
Explanation:
diameter of water hose = 70 cm = 0.7 m
radius = 0.7/2 = 0.35 m
volumetric flow rate Q = 420 L/min
1 L = 0.001 m^3
1 min = 60 s
therefore,
Q = 420 L/min = (420 x 0.001)/60 = 0.007 m^3/s
Area A of fire hose = π = 3.142 x
= 0.38 m^2
<em>From continuity equation, Q = AV</em>
where V1 is the velocity of the water through the pipe, and A1 is the area of the pipe.
Q = A1V1
0.007 = 0.38V1
V1 = 0.007/0.38 = 0.018 m/s.
Nozzle diameter = 0.75 cm = 0.0075 m
radius = 0.00375
Area = π = 3.142 x
= 4.42 x
m^2
velocity of water through the nozzle will be
V2 = Q/A2 = 0.007 ÷ (4.42 x ) = 158.37 m/s
From
<em>F = ρQ(v2 - v1)</em>
Where,
F = force exerted
p = density of water = 1000 kg/m^3
F = 1000 x 0.007 x (158.37 - 0.018) = <em>1108.464 N of force</em>