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Rutgers, The State University of New Jersey

University of Washington

Simon Fraser University

McMaster University

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$^2$ ?

07:43

Kathleen T.

(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?

03:27

Kai C.

(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?

03:02

(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?

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welcome to our fourth and final example video on centripetal forces in this video. Uh, in the last one, I should say, First of all, we looked at how gravity functions as a centripetal force. Well, in this video, then we'll consider the idea of artificial gravity again. This is a physics problem that shows up a lot in different courses, and so it's worth our while to take a look at it here. One of the biggest ideas that people have for how to create quote unquote artificial gravity is to make cylindrical spaceships. If you've ever seen interstellar, they had this idea there, say cylindrical spaceships, where people would live on the edges and it would rotate really fast. Another way you could do this is by having a space center that has some sort of, ah, central hub, usually, how it's pictured. That's then connected out to a ring where people do most of the living out on the ring. If you've seen 2001 Space Odyssey, this is more that style. Either way, the idea is that it's a circular thing, and it spins around really fast with the idea that we want to be able to feel a force on our feet that feels like we're being pushed into the ground the same way that were pushed into the ground here on Earth. So we essentially maintained the same effective weight eso in order to do this, then, if we want to consider here are all of our centripetal forces generated by normal force. So it's gotta be equal to M v squared over r. We want normal force to be exactly as our way is on Earth, so that B m times 9.8 m per second squared EMS would cancel. Which means, given a particular are for one of these things. We would find that V needs to be equal to the square root of our times 9.8 m per second squared or if we had a maximum velocity that we could spin at, we could solve for how large it would have to be. Eso, for example, say we have our that. Let's make it really big here. Let's say we have a radius that's equal to one kilometer we would have 1000 times 9.8, so that comes out to about 10,000. So the tangential velocity would have to be about square root of 10,000 meters per second, rather meter squared per second squared. Here we take the square root of that and you'll be able to find the tangential velocity. By the same token, we could find how fast it would have to spin by saying VT over our so that would be equal to the square root of 10,000 meters squared per second squared, divided by 1000 meters, and you would be able to find how fast this thing has to rotate so clearly. Then it's going to be It's going to be a small omega here, but it could potentially be a very large 10 venture velocity. Would we notice that? No, not necessarily. We would just feel like we're walking on the ground, except that the ground in front of us would be curving up, which might be an odd sensation, but could work in the case of long distance space travel or something like that, where we want to be able to maintain a sense of gravity

Work

Kinetic Energy

Potential Energy

Equilibrium and Elasticity

Energy Conservation

06:27

05:00

04:34

04:09

04:39