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Hope College
University of Sheffield
McMaster University
03:02
Averell Hause
(II) Superman must stop a 120-km/h train in 150 m to keep it from hitting a stalled car on the tracks. If the train's mass is $3.6 \times 10^5$ kg how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman?
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
07:43
Kathleen Tatem
(II) A person has a reasonable chance of surviving an automobile crash if the deceleration is no more than 30 $g$'s. Calculate the force on a 65-kg person accelerating at this rate.What distance is traveled if brought to rest at this rate from 95 km/h?
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welcome to Unit nine on orbital motion in this unit, we're going to discuss things like planets and their motion comets. Anything that we're talking about in the solar system scale, Um will be thinking about those and how they move and why they move the way they do. Um, in order to talk about this, we're going to begin with a little bit of a historical perspective from something called Kepler's Laws. Kepler's laws are very interesting because they're what are called empirical laws. Empirical laws means that essentially, Kepler stared at data for a really, really long time and pulled some patterns out of that data and some laws based on the data thereof. So, um, this is their kind of interesting here. So if you haven't heard of Kepler before, he was an astronomer, and a long time ago, several 100 years ago, and what he discovered were three laws of planetary motion. Um, the first law that he came up with is one you're probably familiar with, and that is that a planet moves around a star not in a circular orbit, but in but in an elliptical orbit with the sun at one of the focuses of the orbit. Okay, Sorry for the weird shaped orbit, but yeah, you get the idea. So elliptical orbits. That's Kepler who came up with this, Uh, his second law was that when you look at these elliptical orbits and you consider the amount of area swept out by a planet in a particular amount of time delta T it turns out that no matter where the planet is in its orbit, so even if it's close to the star instead of far away from the star, it's going to sweep out the same area in the same amount of time. So the two shaded in areas here must be the same if they're swept out in the same time Delta t kind of interesting thing he observed there. And then finally, the third Law. He said that the period of the orbital motion So the time it takes to go around the star or whatever you happen to be ordering is proportional to remember. This simple means proportional to so there's some constant here. It's proportional to the radius cubed the average radius cube. So if we had an average radius for the orbital motion of the Earth and we know that it takes approximately 365 days for it to go around the sun. Then this is the relationship between the radius of that orbit and the period of that orbit. Eso Kepler came up with these three laws and they stood for a while, but no one really knew why. Except that they came from this planetary data that Kepler had looked at. They stood for a long time until we came to something called Newtons Law of Gravitation. And when we had this, we were able to start looking at a lot of other things. Newton started with a pretty simple idea saying, Hey, I think the force that causes thes planets toe all stick together thing is proportional to one over r squared, where r is the distance between the planet and the sun and really the planet and any other body. So any two bodies, they're going to feel a force that attracts them proportional to one over the distance between them squared, and he figured that there would be some mass stuff in there. We're going to take a look at exactly what it was that he came up with see how it relates to Kepler's laws and see how all of the supplies to motion of various bodies in our solar system and beyond.
Fluid Mechanics
Periodic Motion
Mechanical Waves
Sound and Hearing
Superposition
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