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hi guys I have received some questions from you asking how to solve the

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exercises from unit 5 so this video is to help you to understand how to do that

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okay we will start with exercises 11 and 12 from page 125 to do that I remind you

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that definition of average speed the average speed is the distance traveled

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divided by the time taken and the definition of acceleration. The acceleration is the speed

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variation and you know that we write this with the delta letter from the Greek alphabet divided

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by the time taken. Okay so we will start with exercise 11. I'm going to change this to a kind of

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board to write things on it. Just one second please because I'm also trying to get used to

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this way of teaching so okay so exercise number 11 the welding says what variation in speed is

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produced during motion if acceleration is minus 2.5 meters per second square for six seconds

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so i remind you that we are on exercise 11 okay let me check just if okay that's all good okay

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sorry for the interruption and this exercise is on page 125 right so we have

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the data we have for this exercise is that the acceleration is minus 2.5

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meters per second squared okay as you can see is a negative acceleration so

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that means that the speed is going to decrease okay we are in some way

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breaking okay and we are applying this acceleration for six seconds so the

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variation in time is six seconds that's the data we have and the unknown that is

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being asked unknown is the variation in speed so what is the variation in speed

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that's the unknown. What equation we are going to use? Well, the equation we are going to use

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is that the acceleration equals the variation in speed over the variation in time. So we are going

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to solve, try to solve this. So we, as usual, we have an equation and we have different variables

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and we know all of them but one and that one that we don't know is the unknown so

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we have to solve for Delta V and if we solve for Delta V we isolate Delta V so

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Delta T will pass to this side multiplying so Delta V equals a times

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Delta T okay and now next step we have to be careful is the units do we have

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the proper units yes we do so we can continue solving so we write the

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acceleration is minus 2.5 meters per second square multiplied by the time

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that is 6 seconds as you see we can cancel this second with the square and

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we finally have meters per second which are units of our units of velocity and

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Now, if you, I'm taking my calculator,

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if you do that, you will get a result of 15,

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or minus 15 meters per second.

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So that's the variation in speed,

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is minus 15 meters per second.

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And that's the result, okay?

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So the point is that you try to do these exercises,

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you write them in your notebook,

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and later on I will create a task for you to send me with a picture or with a

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scanner or whatever the way is possible for you send me the feedback on the

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things that you are working I will correct them so those that are

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correcting in videos you can upload the correction okay the point is that as the

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platform is not working smoothly yet you will have time to do that so don't get

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stressed continue working but don't worry okay so I hope to see you soon

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later and I will upload a second video for the 12th because I don't want to

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make a heavy or too large video for the platform okay so see you soon bye