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AP Physics 1 Videos 86 videos

AP Physics 1: 2.5 Changes and Conservation Law
445 Views

AP Physics 1: 2.5 Changes and Conservation Law. At what point(s) in this situation is energy lost in any form?

AP Physics 1: 1.4 Waves
181 Views

AP Physics 1: 1.4 Waves. Which of the following is technically true for Max as he stands at the edge of oblivion? 

AP Physics 1: 1.4 Changes and Conservation Laws
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AP Physics 1: 1.4 Changes and Conservation Laws. Find the current across R2.

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AP Physics 1: 2.2 Changes and Conservation Laws 183 Views


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Description:

And now, the moment you've all been waiting for: a stuntwoman refuses to do a stunt and does math problems instead! (The crowd goes wild).

Language:
English Language

Transcript

00:02

All right well here's your shmoop du jour brought to you by hoops. Back in

00:06

the day kids used to play a game by making a hoop roll along the ground by hitting [Child hitting a hoop along the ground]

00:09

it with a stick and we're really happy we didn't live back in the day.. it was really boring... [Man uses his mobile phone]

00:14

A 60kg ball is dropped from a platform, passes through a hoop and then

00:19

it hits the ground. If the platform is 30 meters above the ground and the hoop is

00:24

10 meters above the ground about how fast is the ball falling when it passes

00:29

through the hoop? Our choices are 10,15, 20, 25 meters a second. All right well

00:35

there are different ways to figure this question out, we could use kinematics for

00:38

example or we could actually build this whole set up and break out a radar gun [Picture of a tower that has a hoop attached to the front]

00:43

any policeman around?.. Well that sounds like a lot of work all that including

00:47

the cops. But just having a ball through a hoop isn't that exciting, [Speed gun measures how fast the ball falls through the hoop]

00:51

instead of just a plain old ball let's make this about a high diver and let's

00:55

set that hoop on fire, all right now our diver has to fall through the flaming [Diver appears at the top of the tower and the hoop is now on fire]

01:00

hoop of doom and jump into this tiny pool of water. There you go that's better...

01:04

We'll model this divers motion using conservation of energy, while she's up on

01:09

the platform preparing for her death-defying leap the diver only has [A person bungee jumps from a bridge]

01:12

potential energy, with that good old equation mass times gravity times height.

01:17

When we plug in the numbers and do the math we find the potential energy to be

01:22

18,000 joules. Now once she's actually falling and

01:26

reaches the height of the hoop we can look at a combination of kinetic and [Diver jumps at stops at the flaming hoop]

01:30

potential energy, well the total energy aka mechanical energy still has to

01:34

equal 18 thousand joules. Figure out the potential energy slice of this pie

01:38

first. We're using the same equation and the same numbers except the height has [People take slices of pizza]

01:42

changed so now the potential energy is 6,000 joules, we subtract that number

01:47

from the mechanical energy to find the kinetic energy and we get 12,000 joules.

01:52

Well kinetic energy equals one-half mass times the square of velocity, we know the

01:58

mass and we know the kinetic energy so we can just solve for velocity. Multiply

02:02

each side by 2 and then divide each side by 60 and find that V squared equals 400

02:07

meters a second and when we take the square root of that 400 meters a second

02:12

we end up with a velocity of 20 meters a second also known as

02:16

answer C. When we're dealing with falling objects like this we can use the

02:20

potential energy as a starting point to solve all sorts of variables. We just [Man dodges big boulders falling from above him]

02:25

have to remember how to calculate it and how it relates to mechanical energy and

02:29

kinetic energy. Now we're going to go play with our new favorite app it's

02:33

called 'hoopster', you control a kid from way back who's rolling a hoop along the

02:38

ground with a stick, yeah isn't modern technology great... [Some playing the 'hoopster' game on their phone]

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