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University of Sheffield

University of Winnipeg

McMaster University

03:04

Kai C.

(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?

03:09

Aditya P.

04:39

Muhammed S.

03:27

(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 second example video Talking about power in this video, we're going to consider the idea of efficiency. Efficiency is the concept that when we put some amount of energy into a system, we only get a certain amount back as useful work. So this number is always going to be less than one on all physical systems work this way. For example, there's about 130 mega jewels of energy available in a gallon of gasoline. But the standard car on Lee is about 30 to 40% efficient, so it's not using all of that energy. It's only using about 39 mega jewels of energy per gallon of gas. Now let's compare that to a solar panel, which in the middle of day is receiving approximately one kilowatt per square meter, and we're gonna let this solar panels sit out there for a Knauer. We want to know how Maney solar panels, or how much area of solar panel is required to absorb 39 mega joules of energy. Now, remember solar panels Aaron, also not perfectly efficient. They're only efficient by about 0.2 or 20% efficient. So when we write this down, We say. All right. I want 39 mega jewels. What I have is one kilowatt per square meter. First things first, let's convert from kilowatts. Two watts. I'd also over here. I need to convert this into 39 times. 10 to the sixth jewels. Eso We were convert from kilowatts, two watts, and then we're going to multiply by the amount of time. So that's 3600 seconds, and then we're also going to multiply it by our efficiency of 0.2. And we have our area that we would multiply it by in order to come up on the right hand side with a number in jewels because we've canceled out everything except for Jules. Now we want to solve for a So A in this case is going to be equal to 39 mega jewels divided by 0.2 multiplied by. We have one over 1000 watts times 1/36 100 seconds. And this will give us our area in meter squared. Okay, s so you can go ahead and type that in. It should be, uh, kind of a big number. Not not that big. though I think it'll be on the order of tens of meters squared, and that gives you an idea of how the efficiency of solar panels compares to that of car running on fossil fuel.

Potential Energy

Equilibrium and Elasticity

Energy Conservation

Moment, Impulse, and Collisions

Rotation of Rigid Bodies

04:42

02:20