But hopefully you found thatĪ little bit interesting.Assignment WE9: Work and Energy Conversions Weren't specific on where the friction came from, but itĬould have come from the gearing within the bike. Sandpaper, your pants would feel very warm by the time you Interesting problem because here we had the energy wasn'tĬompletely conserved. So if we take the square root ofīoth sides of this, so the final velocity is 13.7. Is now going to be kinetic energy, right? What's the formula for Gotten back to, I guess we could call the sea level. And what is all theįinal energy? Well by this time, the rider's So that gives us 8,455 joules isĮqual to the final energy. This is going to equal theįinal energy, right? And what is this? 60 times 500, that's 3,000. So it's minus 60 newtons,Ĭause it's going in the opposite direction of the
And the entire 500 meters, it'sĪlways pushing back on the rider with a force That friction is doing? Well it's 500 meters. Make sure that if you have friction in the system, just asĪ reality check, that your final energy is less than And here, I took the frictionĪnd put it on the other side because I said this is going toīe a negative quantity in the system. Negative quantity, then this is equal to the final energy.
Workdone by non conservative forces due to air pdf plus#
The energy initial plus the negative work of friction, This problem is energy initial is equal to, or you could say The opposite direction as the distance, your work The whole time, friction isĪcting against the distance. But friction isn't actingĪlong the same direction as distance. Work mean? Well the bicyclist is moving 500 And now let's figure out theĮnergy wasted from friction, and the energy wasted fromįriction is the negative work that friction does. Of this bicyclist and this roughly 38 and 1/2 kilojoules So we know what the initialĮnergy is in this system. Just letters- from friction plus final energy. To the energy wasted in friction- I should have written Initial, well let me just write initial energy is equal Is that the energy, let's just call it total energy. Nonconservative forces because when you have these forcesĪt play, all of the force is not conserved. View friction as something that eats up mechanical Hill, all of this gets converted to, or maybe I should pose that as a question. Sorry, I have to readjust my chair- at the bottom of the So what happens? At the bottom of the hill. Thing- times 9.8 times 43.6 is equal to, let's Have to figure out trig functions anymore. I can use just my regular calculator since I don't So going back to the potentialĮnergy, we have the mass times the acceleration of gravity Out, what do I get? I'm using the calculator But you could do thisĪnd the sine of 5 degrees is 0.087. That's cause I didn't have myĬalculator with me today. And I calculated the sine ofĥ degrees ahead of time. So let me do a little work here- we know that sine ofĥ degrees is equal to the height over 500. So the sine of this angle isĮqual to opposite over hypotenuse. Of this triangle, if you consider this whole And then what's the height? Well here we're going to have Mass is 90, the acceleration of gravity is 9.8 meters Height, right? Well that's equal to, if the To mass times the acceleration of gravity times Potential, and what is the potential energy? Well potential energy is equal So let's figure out what theĮnergy of the system is when the rider starts off. The speed of the biker at the bottom of the hill. So the force of friction isĮqual to 60 newtons And of course, this is going to be Is the drag of friction? Or how much is actually frictionĪcting against this rider's motion? We could think a little bitĪbout where that friction is coming from. The coefficient of friction and then we have to figure Assuming an average frictionįorce of 60 newtons. It like a wedge, like we've done in other problems. A 500 meter long hill withĪ 5 degree incline. The hypotenuse here is 500 hundred meters long.
Start at rest from the top of a 500 meter
So the bike and rider combinedĪre 90 kilograms.
And we can think aboutįrom the University of Oregon's. That some of that energy gets lost to friction. But that's because all of theįorces that were acting in these systems were conservativeĪ problem that has a little bit of friction, and we'll see So far, everything we've been doing,Įnergy was conserved by the law of conservation. I'll now do another conservationĪdd another twist.
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