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Ex 12 page 125

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Subido el 19 de marzo de 2020 por Segismundo P.

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Hi guys, some of you have requested me to send you more exercise solved, because you are having problems to solve exercise 12 and 13. 00:00:02
So we will start with number 12. 00:00:10
The wording says, at a specific moment, the speed of a moving object is 45 km per hour. 00:00:14
So we will start by writing the data. 00:00:22
so this is exercise 12, page 125. The data we have is that the velocity at the end of a motion is 45 00:00:24
kilometers per hour, ok? And then it says if you began studying the motion one minute earlier, so 00:00:43
the time that we've been studying the motion is one minute, okay, we write it 00:00:51
here in the data, and the acceleration, which is constant, is 20 centimeters per 00:00:56
second squared, so we write the acceleration 20 centimeters per second 00:01:02
squared. What is the initial speed? So the unknown is the initial speed, so v1, of 00:01:09
of the interval studied. What will the value of the speed be after one minute or another minute? 00:01:20
So that's the second part that we will solve after finishing this. 00:01:28
So the first thing that we observe here is that we have different units, and none of them is an international system unit. 00:01:34
So the first step would be to convert these units into international system units. 00:01:43
So, we write a first conversion factor, we write kilometers in the denominator and meters in the numerator, a 1 and a 1000, and for hours, we write hours in the numerator and seconds in the denominator, and 3600, okay? 00:01:51
So, if you calculate, well, now hours cancel with hours, and we can get rid of kilometers in this way, and we have meters per second. 00:02:10
And if you do this operation in your calculator, you will get a result of 12.5 meters per second. 00:02:21
ok then the delta time is in minutes and we should have it in seconds well one 00:02:30
minute by the way is 60 seconds we don't need to use conversion factor for for 00:02:40
that and then 20 centimeters per second square we need to convert that into 00:02:45
meters per second square so we write centimeters in the denominator meters 00:02:50
numerator 1 and 100 we get rid of the centimeters and finally we have 00:02:54
0.2 meters per second squared, okay? So once we have all the data in the 00:03:01
international system we will start by, I'm going to delete this part here, we will 00:03:11
start by solving this. So we write a solution now. For that we need to know 00:03:18
what is the equation we are going to use, okay? And we are going to use the 00:03:28
equation of the acceleration the solution says that is the speed variation over the 00:03:31
time taken okay so and and this speed variation is always the final speed 00:03:39
minus the initial speed over the time taken so we know the acceleration we 00:03:47
know the final speed and we know the time taken so yes we need to solve for 00:03:53
v1 or isolate v1. So we write the acceleration 0.2 meters per second 00:03:59
squared, that's just by substituting in this equation v2 is 12.5 meters per 00:04:05
second minus v1 over 60 seconds. Okay the first thing we can do is to pass this 60 00:04:14
seconds okay from this point to this multiplying so we will do that and now 00:04:25
we have that 12.5 meters per second minus the initial speed equals 0.2 meters 00:04:35
per second square times 60 seconds so we cancel this with the square and we 00:04:45
finally have units units of speed and now we do 60 times 0.2 is 12 meters per 00:04:53
second and now we can pass V1 to the right and 12 to the left so we will have 00:05:04
finally 12.5 meters per second minus 12 meters per second and that gives an 00:05:12
initial value of 0.5 meters per second for the initial speed so we write the 00:05:22
result okay so that's the the end of the first part and now we have a second part 00:05:29
in the second part the wording says that what will the value of the speed be 00:05:38
after another minute so now we we could have V1 and V2 for the second 00:05:45
but in the second part what we are going to do is use the v2 we have in the first part 00:05:51
that it was 12.5 meters per second 00:05:56
and we are going to calculate a final speed so we could call that v3 for example right 00:06:03
that's the unknown so now the equation we are going to use a equals the variation speed so v3 00:06:10
minus v2 over the time that it continues being one minute or 60 seconds in this 00:06:20
case so we write 0.2 00:06:28
gosh sorry for that 00:06:32
0.2 meters per second square times 60 seconds which is again 12 as we did 00:06:35
before and now is v3 minus v2 that is 12.5 meters per second and we get a value 00:06:51
of 12 meters per second equals v3 minus 12.5 meters per second if we pass to 00:07:07
these these to this side summing up we will get a result of 24.5 meters per 00:07:16
second okay and that's all for the exercise 12 okay you have any doubt you 00:07:28
can use the discussion forum or which is in Spanish for the dudas okay and then I 00:07:36
I will answer your doubts, but if any of you want to answer doubts to other peers, you can do it, and this would be a way of continuing with our collaborative work. 00:07:45
By the way, that would be part of your final mark, so if you contribute to solve any doubt, that would be positive for your grade. 00:07:56
Okay, so thank you for your attention and later on I will upload other video for exercise 13. See you! 00:08:08
Idioma/s:
es
Autor/es:
Segismundo Peláez
Subido por:
Segismundo P.
Licencia:
Reconocimiento - No comercial - Compartir igual
Visualizaciones:
90
Fecha:
19 de marzo de 2020 - 12:10
Visibilidad:
Público
Duración:
08′ 21″
Relación de aspecto:
1.78:1
Resolución:
1364x768 píxeles
Tamaño:
12.75 MBytes

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