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AP Physics 1: 3.1 Changes and Conservation Laws 196 Views


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Description:

If you bang your head against a moving wall while studying physics, and your head sticks to the wall and keeps moving, what is the combined velocity of the wall and your sad, over-taxed head?

Language:
English Language

Transcript

00:03

All right well here's your Shmoop du jour brought to you by collisions [Two cars collide with each other]

00:06

physicists are always dealing with collisions sometimes that collision is

00:10

their head colliding with a wall over and over again trust me i have been there a [Physicist repeatedly banging his head on a chalkboard]

00:14

particle with mass 1.5 grams moves with a velocity of negative 2 meters a second

00:19

when it encounters a three gram particle moving to the left at a velocity of 4

00:25

meters per second the two particles stick together and continue to move what

00:29

is their combined velocity here are choices [Muttering of potential answers]

00:33

Alright, well two particles collide stick together

00:37

that's right we're dealing with an inelastic collision and we're stoked [Two particles colliding and sticking together]

00:41

like a dream come true granted we have strange dreams there was

00:46

this one where we were riding a dinosaur into a tunnel and never mind actually [Two people riding on a dinosaur into a tunnel]

00:50

yeah, let's just get the question all right when we're dealing with an

00:53

inelastic collision like this we have to remember that momentum is always

00:57

conserved it's like there's a law about it or something so the total momentum of

01:02

two particles before the collision has to equal the total momentum of the

01:06

particles after the collision and we know that momentum equals mass times [Two particles stuck together above a definition of momentum]

01:11

velocity we'll call these particles one and two - that's creative right well here's

01:16

the equation this says that mass times velocity of particle 1 plus the mass

01:21

times velocity of particle 2 equals the sum of the mass of both particles times [equation for the velocity of two particles]

01:27

the final velocity we can flip going to decide which particle in this problem is

01:32

1 and which is 2 we'll say the particle with the negative velocity is numero uno

01:36

and now we can plug in the numbers 1.5 grams times negative 2 meters a second

01:41

Plus 3 grams times 4 B to the second equals 4.5 grams times final velocity

01:47

well solve them for final velocity gives us answer of 2 meters of seconds and the [equation filled in with the mass and velocity readings]

01:53

answer B is correct if you ever feel like banging your head against a wall

01:56

just stop take a few deep breaths and maybe take a study break because [woman stops a man from beating his head against a wall]

02:00

studying physics can get frustrating sometimes but studying physics with a

02:03

concussion, well that won't work yeah [Boy studying physics falls off chair]

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