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goldenfox [79]
2 years ago
8

The security alarm on a parked car goes off and produces a frequency of 960 Hz. The speed of sound is 343 m/s. As you drive towa

rd this parked car, pass it, and drive away, you observe the frequency to change by 75 Hz. At what speed are you driving
Physics
1 answer:
Greeley [361]2 years ago
7 0

Answer: 13.4\ m/s

Explanation:

Given

The frequency of the source is f_o=960\ Hz

Change in frequency is 75\ Hz

Speed of sound c=343\ m/s

Suppose v is the velocity of the observer

Doppler frequency is given by

f'=f_o\left(\dfrac{c\pm v_o}{c\pm v_s}\right)

Here, the source is at rest

While approaching source, frequency is

f_1=f_o\left(\dfrac{c+v}{c}\right)\quad \ldots(i)

While leaving, frequency is

f_2=f_o\left(\dfrac{c-v}{c}\right)\quad \ldots(ii)

The difference in the frequency is

\Rightarrow f_1-f_2=75\\\\\Rightarrow f_o\left(\dfrac{c+v}{c}\right)-f_o\left(\dfrac{c-v}{c}\right)=75\\\\\Rightarrow f_o\left(\dfrac{2v}{c}\right)=75\\\\\Rightarrow v=\dfrac{75\times 343}{2\times 960}\\\\\Rightarrow v=13.39\approx 13.4\ m/s

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3.88 * 10^(-15) J

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A boy throws a ball of mass 0.22 kg straight upward with an initial speed of 29 m/s. When the ball returns to the boy, its speed
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Answer:

The work is -67.76 J

Explanation:

The law of conservation of energy is considered one of one of the fundamental laws of physics and states that the total energy of an isolated system remains constant. except when it is transformed into other types of energy.

This is summed up in the principle that energy can neither be created nor destroyed in the universe, only transformed into other forms of energy.

In this case you must calculate the loss of kinetic energy. This loss is actually the work done against the resistive force in the air. Friction is the only force other than gravity that acts on the ball.

So, the loss of kinetic energy is \frac{1}{2} *m*(vf^{2} -vi^{2} )

You know:

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Final velocity of the ball: vf= 15 \frac{m}{s}

Replacing:

\frac{1}{2} *0.22 kg*(15^{2} -29^{2} )= -67.76 J

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<u><em>The work is -67.76 J</em></u>

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