Sound waves must have intensity if a person is to hear them. a. True b.

Sound waves must have intensity if a person is to hear them. a. True b. False

2 months ago

Solution 1

Guest Guest #4140
2 months ago


a. True


Intensity is what we commonly call Volume, sound waves with no intensity or volume wouldn´t be hearable by humans, so the statement would be True, Sound waves must have intensity if a person is to hear them. The most usual unit to measure sound intencity is Decibels, and  a person with good ears can hear up to -15 dB.

Solution 2

Guest Guest #4141
2 months ago
The answer is  
A, True            

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Solution 1

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Solution 1
Applicable formular:

F = Gm1m2/d^2, where F = gravitational force, m1 & m2 = mass of the two bodies, G = Gravitational constant, d = distance between the bodies.


8.64*10^-8 = (6.67*10^-11*90*90)/d^2
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Solution 2




-a p e x

I would love to stretch a wire from our house to the Shop so I can 'call' my husband in for meals. The wire could be tightened to have a tension of 240N and a m/L 'weight' of 0.05kg/L. How long would it take for my pulse wave to travel to the Shop (24m) to ring a bell to indicate dinner time.
Solution 1
Note: I'm not sure what do you mean by "weight 0.05 kg/L". I assume it means the mass per unit of length, so it should be "0.05 kg/m".

The fundamental frequency in a standing wave is given by
f= \frac{1}{2L} \sqrt{ \frac{T}{m/L} }
where L is the length of the string, T the tension and m its mass. If  we plug the data of the problem into the equation, we find
f= \frac{1}{2 \cdot 24 m} \sqrt{ \frac{240 N}{0.05 kg/m} }=1.44 Hz

The wavelength of the standing wave is instead twice the length of the string:
\lambda=2 L= 2 \cdot 24 m=48 m

So the speed of the wave is
v=\lambda f = (48 m)(1.44 Hz)=69.1 m/s

And the time the pulse takes to reach the shop is the distance covered divided by the speed:
t= \frac{L}{v}= \frac{24 m}{69.1 m/s}=0.35 s
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Solution 1
The correct answer is
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In fact, the relationship between frequency, wavelength and speed of a wave is given by
\lambda= \frac{v}{f}
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The speed v of a wave depends only on the properties of the medium; in this problem the medium does not change, so the speed remains the same. 
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The absolute difference between two frequencies is referred to as beat frequency. That is,
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In this case, the frequency of unknown fork must be between 240 Hz and 250 Hz. Then,

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Therefore, the unknown frequency is 244 Hz.