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Kathleen Tatem
(II) According to a simplified model of a mammalian heart, at each pulse approximately 20 $g$ of blood is accelerated from 0.25 m/s to 0.35 m/s during a period of 0.10 s. What is the magnitude of the force exerted by the heart muscle?
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(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?
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(I) A constant friction force of 25 N acts on a 65-kg skier for 15 s on level snow.What is the skier's change in velocity?
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welcome to our next unit, where we'll be discussing the sources of magnetic field. Now we've already looked at the force due to magnetic field, the source of magnetic field. It turns out to be well, you'll see that is very much related. Um, it was discovered by a guy named or Stead, uh, that electricity and magnetic field have a relationship with each other. He What he did was he had a current carrying wire and he set a compass next to it. This is actually in a demonstration in lecture with some students, where he was attempting to demonstrate that these things were not related. And when he set up the compass next to the wire, he found that the needle didn't change direction until one of his students walked up and rotated the compass and found that the needle reoriented itself once again to not point in the North direction but to point in some direction related to the current. When he turned off the current, the needle returned to true north, um, and thus he was able to find that somehow the compass needle was being affected by the current Onda. Reason for that is that current produces magnetic field or better said a moving charge produces magnetic field, so moving charge creates a magnetic field. It does so according to something called the Boats of Art Law, which can be written like this you have be due to a point. Charge is equal to the constant Muna over four pi multiplied by Q The across our hat. That's right. That's a unit vector that were crossing with their divided by r squared. So we'll talk more about the implications of this law as we get into the video. But for now, you should know that magnetic field can be created by moving charge. Another way that we can create magnetic field is a way that you've probably seen before, which is with permanent magnets. You're familiar likely with the bar magnets that have a North Pole and a South Pole. And how you can connect these magnets with other magnets which would be connect like this with North attracted the South. Um, now, if you tried to put south next to South, they repel each other. And the reason for this is that these bar magnets are producing, uh, die pole magnetic field. Okay, eso If we were to draw a picture of this, then we would say that there is some magnetic field here that is being produced. Now this thing can be modeled as a magnetic di poll moment. If you remember, we call that Mu in the last video and we found it based on a loop of current. Well, it turns out that permanent magnets have ah lot of very small regions with aligned magnetic dipole moments due to the structure of the molecules that make up the magnet. So these things all have a very small magnetic day, Paul. And if they all line up, it means that they all have an editing, a superimposed you could even say magnetic field. And if you add up enough of them all in the same direction, you'll get a strong magnetic field coming out of this particular magnet. You can even apply a strong magnetic field to an object that has disorganized magnetic die polls. And when you apply this magnetic field, all those magnetic die polls well, actually line up two point in the same direction as the applied magnetic field. Okay, so these are a few characteristics about how permanent magnets work. We're going to focus more on what we talked about previously. Which is that moving charge produces magnetic field because we have this types be OTs of art law that we can use to analyze the situation.
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