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University of Washington

Simon Fraser University

Hope College

University of Sheffield

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Muhammed S.

(I) A 7150-kg railroad car travels alone on a level frictionless track with a constant speed of 15.0 m/s. A 3350-kg load, initially at rest, is dropped onto the car. What will be the car's new speed?

Aditya P.

00:39

Averell H.

I) How much tension must a rope withstand if it is used to accelerate a 1210-kg car horizontally along a frictionless surface at 1.20 m/s$^2$ ?

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welcome to the next section in unit 12. And this section will be talking about intensity and and also decibels. Yeah. Okay. So, thes airways that we are able to characterize waves according to the amount of energy that they're transferring toe a material. So, for example, intensity is defined as power divided by area. Okay, so this is the intensity of a wave. It's the amount of energy delivered per unit time per unit area. Remember that power is equal to energy per unit time. Okay, so this is what intensity is defined as you've probably used it in some some sense before, Such as the sun is very intense today, or something like that, or that sound is very intense. And that would be a correct usage of the word intense because it is applied to the amount of power delivered by a wave per unit area. So if we're thinking about, for example, a star and the intensity of its light coming out okay. One issue here is that if we think about it, produced has some power with which it produces light, but it's producing it in every direction. Can't just think two dimensionally here you have to think spherical e. Okay. And over here, all we care about is what specifically is hitting the earth. Okay. And so we'd worry about a surface area over here on the earth or wherever we might be interested. But the sun is generating all of this, So we need to think about well, I have I And then my area, really, in this case is going to be equal to the power provided by the sun divided by four pi r squared, which is the surface area of a sphere. Okay, So because all of the power is distributed across that spherical area, we have to divide it by four pi r squared in order to get the intensity now are being very large between the sun and the earth. That's going to reduce it significantly. And that's why we don't all burn up because of the sun. On the other hand, if we're thinking about sound, for example, if you have ah, think about a speaker on a pole in the middle of the field and it starts pulsing to create eyes and lows and the pressure around it again, we have this spherical pattern where the disturbance to the air around. It is going to move out away from its satirically thes air what are called spherical waves. And they abide by this idea that I is equal to P over four pi r squared, though don't forget that, really. It comes from Thean definition of intensity, which is that it is the power delivered, divided by the area. Now with sound intensity. People have looked for ways to categorize this or for a long time, and the way they've done it is with this unit of decibels. You have perhaps heard of decibels before. It's the way that we measure the volume of sound, so a decibel is actually an empirical scale. It says that the number of decibels we have is equal to 10 decibels multiplied by log, so that's based 10 log of some intensity eyes. That's the intensity that you perceive divided by some standard intensity China. Now I know it's supposed to be the minimum intensity that a human ear can detect. Case that's approximately one times 10 to the negative 12 watts per meter squared. Those would be our units of intensity. Power is in Watts area. Isn't meter squared Okay, so having this is a guy, then we can calculate the number of decibels that we're perceiving. And then we also might have to apply our definition. I equals p over a or equivalently four spherical waves eyes equal to P divided by four pi r squared. So let's see some examples of this.

Superposition

Thermal Properties of Matter

The First Law of Thermodynamics

Kinetic Theory Of Gases

The Second Law of Thermodynamics

01:50

02:50

04:23

01:27

05:49

02:12

02:35

04:09