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AP Physics 2 Videos 59 videos

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AP Physics 2: 1.1 Systems Interactions and Changes 166 Views


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AP Physics 2: 1.1 Systems Interactions and Changes. How much heat is dissipated due to air drag as the candy falls?

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English Language

Transcript

00:00

Thank you here's Your shmoop du jour brought to you

00:05

by national candy day which is on november fourth We

00:09

consider the other three hundred sixty four days of the

00:11

year to just be well personal candy days to celebrate

00:14

national candy day Willy wonka planes to drop bags of

00:17

sweets from an airplane Unfortunately he forgot to take into

00:20

account the heat produced by drag forces as the bags

00:24

fall through the air Well if the candy bags have

00:27

a mass of zero point four kilograms and reached terminal

00:29

velocity of twenty five meters per second how much heat

00:32

is dissipated due to air drag for every ten meters

00:36

that the candy falls fine here The potential answers While

00:42

dropping bags of candy from a plane sounds awfully generous

00:46

it also sounds like a good way to give people

00:48

brain trauma You've heard of ice cream headaches but candy

00:51

concussions are a new thing We'll assume willy gets lucky

00:54

and doesn't hit anyone directly let's think back to a

00:57

long time ago when we were learning about potential and

01:01

kinetic energies We know that potential energy equals mass times

01:04

height times gravity and we know that kinetic energy equals

01:07

one half mass times velocity squared How do we know

01:10

that Well we studied a bunch of this really cool

01:13

website Uh i can't remember the name but shoot It

01:16

was like shoe or smooth or something like that Anyway

01:20

the moment before an object falls all of its energy

01:22

is stored as potential energy and the moment before an

01:25

object hits the ground All of its energy is in

01:28

the form of kinetic energy moving in a perfectly frictionless

01:31

system The total energy at each of these moments has

01:34

to be equal and put it in terms of work

01:37

A force gravity is applied to an object the bag

01:40

of candy causing it to move the change in kinetic

01:44

energy equals the work done but we don't exist in

01:48

a perfectly frictionless system We exist on planet earth which

01:51

has an atmosphere when we're very grateful for it As

01:54

an object falls through the air it encounters friction also

01:57

known as drag because we're used to rubbing our hands

02:00

together deviously while hatching an evil seem way know that

02:03

friction causes some kinetic energy to transfer into heat energy

02:08

so now we have to throw heat into the equation

02:11

Now our equation shows that the change in potential energy

02:15

equals the change in kinetic energy plus heat When a

02:19

falling object reaches terminal velocity it has stopped accelerating which

02:25

means there's no more change in velocity which means that

02:28

there is no change in kinetic energy So at that

02:31

point all the work being done is creating heat not

02:34

changing the velocity All the change in potential energy equals

02:39

heat energy Now we can plug in the numbers get

02:42

an answer and go eat some candy and start this

02:44

whole questions giving us some serious sugar cravings once an

02:47

object has reached terminal velocity that he created in a

02:50

ten meter fall equals mass times gravity times the change

02:53

in height the mass of the bag equals zero point

02:55

Four kilograms Little round gravity up to ten meters per

02:59

second squared and a change in height is ten meters

03:03

Will the mass shows that the heat created equals forty

03:06

jewels Will answer D is correct We can see that

03:11

once an object reaches terminal velocity whatever the velocity is

03:14

doesn't affect the heat created Get the bags are falling

03:17

at one meter per second or one hundred meters per

03:20

second The work done is the same And if we

03:22

ever see a bag of candy plummeting out of the

03:24

sky and heading for a skull will take cover And

03:27

then we'll scavenge that candy off the ground like animals 00:03:30.67 --> [endTime] That's Just how we roll

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