Answer:
r = 2.63 m
Explanation:
To find the distance at which the sound level is 120dB, you first calculate the intensity of the sound. You use the following formula:
(1)
β: sound level = 120dB
I: intensity of the sound
Io: threshold of hearing = 10⁻12W/m^2
You solve the equation (1) for I and replace the values of all parameters:
![\beta=log(\frac{I}{I_o})^{10}\\\\10^\beta=10^{log(\frac{I}{I_o})^{10}}=(\frac{I}{I_o})^{10}\\\\I=10^{\beta/10}I_o](https://tex.z-dn.net/?f=%5Cbeta%3Dlog%28%5Cfrac%7BI%7D%7BI_o%7D%29%5E%7B10%7D%5C%5C%5C%5C10%5E%5Cbeta%3D10%5E%7Blog%28%5Cfrac%7BI%7D%7BI_o%7D%29%5E%7B10%7D%7D%3D%28%5Cfrac%7BI%7D%7BI_o%7D%29%5E%7B10%7D%5C%5C%5C%5CI%3D10%5E%7B%5Cbeta%2F10%7DI_o)
![I=10^{120/10}(10^{-12}W/m^2)=1\frac{W}{m^2}](https://tex.z-dn.net/?f=I%3D10%5E%7B120%2F10%7D%2810%5E%7B-12%7DW%2Fm%5E2%29%3D1%5Cfrac%7BW%7D%7Bm%5E2%7D)
Next, you use the following formula for the power of the sound with intensity I, and you solve for r:
![I=\frac{P}{4\pi r^2}\\\\r=\sqrt{\frac{P}{4\pi I}}](https://tex.z-dn.net/?f=I%3D%5Cfrac%7BP%7D%7B4%5Cpi%20r%5E2%7D%5C%5C%5C%5Cr%3D%5Csqrt%7B%5Cfrac%7BP%7D%7B4%5Cpi%20I%7D%7D)
r: distance at which the sound level is 120dB
P: power of the sound = 87W
I: intensity of the sound = 1W/m^2
You replace the values of I and P for calculating r:
![r=\sqrt{\frac{87W}{4\pi (1W/m^2)}}=2.63m](https://tex.z-dn.net/?f=r%3D%5Csqrt%7B%5Cfrac%7B87W%7D%7B4%5Cpi%20%281W%2Fm%5E2%29%7D%7D%3D2.63m)
The distance is at 2.63m from the source of the soundr = 2.63m
The car is moving with constant velocity (so, constant speed in a straight line)
Explanation:
Acceleration is defined as the rate of change of velocity:
![a=\frac{\Delta v}{\Delta t}](https://tex.z-dn.net/?f=a%3D%5Cfrac%7B%5CDelta%20v%7D%7B%5CDelta%20t%7D)
where
is the change in velocity of the object
is the time taken for the velocity of the object to change by ![\Delta v](https://tex.z-dn.net/?f=%5CDelta%20v)
In this problem, we have car moving with an acceleration of
![a=0 m/s^2](https://tex.z-dn.net/?f=a%3D0%20m%2Fs%5E2)
This implies that
![\Delta v = 0](https://tex.z-dn.net/?f=%5CDelta%20v%20%3D%200)
So, the velocity of the object is constant. However, velocity is a vector quantity: so it has both a magnitude (the speed) and a direction. Since the velocity here is constant, this means that both the speed and the direction must be constant: and this is possible only if the car is moving with constant speed in a straight line.
Learn more about acceleration:
brainly.com/question/9527152
brainly.com/question/11181826
brainly.com/question/2506873
brainly.com/question/2562700
#LearnwithBrainly
Answer:
When the bar magnet is withdrawn from inside the coil, again an induced current is setup in the coil due to change of magnetic field through it. As a result galvanometer gives a deflection in the reverse direction
Answer: reduced greenhouse gases
Explanation:
The use of tides for energy is known as tidal energy. This is a type of energy that can be renewed. It results when gravitational fields from both the sun and the moon, combined with the earth’s rotation around its axis, causes high and low tides. The advantages of tidal energy includes:
- it is a renewable energy,
- it us environmental friendly: this is so because it dosent emit any climate gases
(example, carbondioxide)that can cause green house effects.
Green house effects occurs when green house gases such as carbondioxide traps in heat from the sun and cause a gradual rise in earth's atmospheric temperature.