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03:04

Kai Chen

(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?

04:39

Muhammed Shafi

01:24

Keshav Singh

(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?

0:00

Aditya Panjiyar

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welcome to our second example of video on two dimensional motion in this video, considered the difference between velocity and speed when we're talking about two dimensional motion So velocity and speed, you may recall that velocity is a vector where I speed is not a vector. So whenever I want to write my velocity, I'm gonna need components. I may have 14 m per second the I hat minus well meters per second in the J hat and now we ask ourselves Well, what what corresponds to the speed here? Well, if I were to draw out this factor, I'd say Okay, I have 14 m per second this way. Then I have negative 12 m per second. Communities pointed down and so the vector V looks like this. So that's what my velocity looks like. We'll speed, remember is related to velocity, except it doesn't care about direction. So the quantity here that we can report for V that doesn't care about direction is its magnitude. Remember, there's two ways to report it. One is we can write it velocity and component form. The other one is we can write it in our magnitude, an angle form. So we're going to calculate the magnitude here should be 14 m per second squared plus negative 12 meters per second all squared. And when I do this calculation, I'm going to get out of this speed. So are two dimensional speed, then is defined by the magnitude of our velocity vector. So this is the principal difference between the velocity and the speed. Now it could get a little more complicated if we were to stay right velocity as a function of t. So say we had, um six meters per second t in the I had direction minus one meter per second. We have to call the 6 m per second squared to get our units right and then we have 1 m per second squared times t squared in the J hat direction and we want to find out Well, what's what's our speed gonna be? Hasn't changed. It's still going to be the magnitude of the velocity vector. It's just that in this case, the magnitude of the velocity vector is going to include a couple of variables, so we'll have 6 m per second squared times t squared in this case because he was inside plus and we'll have negative 1 m per second squared times t to the fourth because that also got squared. So now we have a Nick Waysh in for our speed. It will depend on what time it is, just like how our velocity is varying with time. Our speed also varies with time. So not particularly tricky to figure out. We just wanna make sure that we're always tracking that speed is going to be calculated using this magnitude formula that we've had or the Pythagorean theorem, as many of my students like to refer to it as.

Newton's Laws of Motion

Applying Newton's Laws

Work

Kinetic Energy

Potential Energy

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