Projectile Motion Example - How fast when it hits the ground

Launch a projectile from the top of a building. How fast is it going when it hits the ground?

[@natalieschwarz1932]

His skills with writing equations backward is mind boggling.

[@yoprofmatt]

If only those were actual skills and not just a simple trick. See www.learning.glass Cheers, Dr. A

[@ohbeuri7857]

Omg I thought you just mirrored the vid 😱

[@lungintshangase4488]

The advantage he's left handed

[@trevorokoth6469]

He's not writing backwards😂🤣🤣 it's the software

[@coolperson1412]

I think the vids just fliped

[@spivak4342]

By the way he did an input mistake. He said that he will take Vi as 20 m/s but he used 30 m/s instead

[@tomtommyle]

This is correct. At 1:06, he states V_i= 20 m/s. Final velocity should be 35.80 or 36 m/s when rounded to significant digits after using the correct initial velocity of 20 m/s.

[@eddysonaltidor3791]

Thank the lord!

[@mojave7025]

Thank you for catching that. I was thinking he was using the 30^2 (Theta) as Vi and it was confusing me.

[@gebrokenwilde3405]

i was wondering why i got it wrong, glad im not the only 1 who was confused about the 30

[@manuboker1]

Wonderful lecturer that makes physics fun and understandable !!!

[@dvnsyaswanth9936]

sir, you could have solved the problem faster if you divided Vi into Vix and Viy. from Viy you could have solved for time(2Viy/g+kinematic equation for distance) and then plug in the time value to get Vfx (which is the same) and Vfy from one of the kinematic equations . Anyway, your videos are really great .

[@Mikey-qr6tt]

I wish have a teacher like you Sir

[@electrolyteorb]

Sir please take a look: A projectile is thrown from ground with velocity 8 m/s. When it is moving with 6 m/s, it is at maximum separation from the point of projection corresponding to the speed 6 m/s. Then this maximum separation corresponding to speed 6 m/s is k meter. Find the value of k

[@justinamaynard90]

There's something in the equation I don't get... Vfinal=sqrt(Vinitial^2+2gh) >> Vfinal=sqrt(30^2+(9.8)(45)). Why was Vinitial substituted by 30? Wasn't it supposed to be 20 m/s? Thanks for clarifying.

[@yoprofmatt]

Justina, Ah, excellent catch! Yes, there was a mistake at the 7:11 mark. Should have used 20 m/s for Vinitial. Well done. Cheers, Dr. A

[@meggileskirbytupaz]

Thank you for clarifying this. My students also noticed this. ❤️❤️❤️

[@sakshammane6932]

His skill is mind blowing.

[@sakshammane6932]

His skill is bind blowing.

[@rishiaman2288]

this makes so much sense

[@yoprofmatt]

Excellent. Hopefully that continues. Cheers, Dr. A

[@ethiomusiclyrics5318]

Great teacher

[@shahadalmahrazi533]

Im just thinking about it, its 8 years ago and I'm just watching it now

[@chabanemoumani8926]

Very very nice teaching thank you so math ❤

[@moiseslobopvh]

Hello teacher. How can I find the shooting angle of a ball to hit a basketball hoop, if I have the speed, gravitational acceleration and vertical and horizontal distances? I can't deduce an equation to find the angle when the target is above the launch point.

[@Roberto97810]

I'm still trying to rationalise this situation, is he behind the glass and if yes how is he able to write and draw with such pinpoint accuracy?🤐🇿🇦🙆🏽‍♂️

[@sonkemctan8187]

There is no influence made by an angle that is equal to 30 degrees to the V initial?

[@yoprofmatt]

Correct. If the question is just about final speed, the initial launch angle is irrelevant. However, if you asked a different question, such as how long is it in the air, then the initial launch angle does come into play. Thanks for the question. Cheers, Dr. A

[@AB-lt8my]

Matt Anderson thanks sir

[@birenderhooda5217]

Where are you writing sir I am confused why you take 30 in place of 20 its wrong or not?

[@nicole_playsgamez]

THANK YOU! i thought i was wrong lmao

[@borisdasgupta2170]

Professor Anderson. Thank you for the wonderful lectures. I comprehend them completely but I couldn't completely understand a part of it i.e. why is Vyf the same as Vyi in the example that you gave us to understand the concept. I concur with you for Vxi=Vi=Vxf as there is no specific acceleration provided that we ignore the air resistance but in the y coordinate the object does undergo an acceleration due to gravitational force while moving downwards.

[@yoprofmatt]

What time point in the video? Cheers, Dr. A

[@borisdasgupta2170]

@@yoprofmatt 10:00 in the video why is the final velocity at the ground the same as the i itial velocity with which you throuw it against it

[@lappelduvide2515]

Hello Dr, when do we ignore the negative sign of gravity when calculating? I noticed when you substituted the values while getting the square root of Vi^2+2gh that gravity is written as 9.8 and not -9.8. I get that it's so we don't get an error when calculating because it's a square root, but what's the concept behind this? I hope someone answers. TIA!

[@lappelduvide2515]

Also, does the formula Vf = sqrt(Vi^2+2gh) apply to all forms of projectiles? Would be really neat if it did.

[@vav5838]

hey that's because h is also negative due to the nature of displacement. it will turn out to be positive when multiplied with negative g. sorry i just realized i'm seven months late but i'll comment for the heck of reinforcing it in my head

[@mjmeternal2696]

We never ignore the sign. It's always negative 😉

[@nuhibrahim215]

Superb!

[@asrithkatragadda6891]

so helpful thx a lot

[@abdullahtarek2560]

Hi prof. Why did you choose the gravity -9.8 since the object rise then falls as it moves with direction of gravity then against it

[@sawineta4293]

How does Vi change from 20m/s to 30m/s??

[@yoprofmatt]

Because I made a mistake, that's how. Great catch. Cheers, Dr. A

[@murphygreen8484]

How does the angle not matter? If I throw the ball down it will hit with a higher velocity then if I throw it up and let it fall down, right?

[@gauravGupta-bk2sw]

You can either "throw" a ball up OR "let" it fall down, but you can't do em together. I hope you understand the HUGE difference between the two. If you do, your doubt will get cleared, BTW your statement is wrong!

[@haifasaeed5221]

how can i contact you professor? i have a physics problem i'm studying for my final and it's really necessary 😢

[@Rachel-re9ge]

I calculated the time to be t=1.45 s but negative. Could you clarify how I may have accidentally obtained a negative? Thank you. I used the kinematic equation without acceleration: y=yinitial + 1/2(Vinitial + Vfinal)t

[@justinmalik6977]

Rachel Barocio see if you have to divide time by something with negative

[@yoprofmatt]

Try this video and see if it helps: kzbin.info/www/bejne/kIHEg3molJiaaM0 Cheers, Dr. A

[@ksdnsdkumar1375]

What is that screen he is writing on? How can he writes backwards?

[@kipngetichkelvin7332]

the lesson was nicely enjoyed by kelvin kipngetich

[@yoprofmatt]

KIPNGETICH KELVIN, Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@fizixx]

Excellent

[@yoprofmatt]

Cheers, Dr. A

[@ahmedroushdy5541]

i think under the square root the value of Viy should be Vi cos not 30 squared

[@dheerajsharma355]

We did this in 11th standard

[@jackysu1329]

At 2:58 how did he take away the 2 that was next to the acceleration from the original kinematic equation

[@RM-zd9ew]

cuz acceleration is 0 in the x direction. so a = 0

[@vish4617]

vf= 35.81 m/s t=3.23 s i hope im right cuz ive been studying for an exam soon..

[@anoopsinghanoop2060]

Where he is writing

[@qaiserrehamminhas7149]

i am kiran from pakistan.and sir is there any easy way to leran about projectile motion because its so difficult topic for me to understand ?

[@zynex9250]

How to solve it without initial velocity?

[@elijahsekeleti7061]

wow am enjoying the lessons # EJ

[@s0ap388]

is this formula also applicable in zero launch angle?

[@yoprofmatt]

Yep. Cheers, Dr. A

[@surajitbosu8639]

very nice teaching

[@yoprofmatt]

Thank you. I enjoy it. Cheers, Dr. A

[@terminator9009]

how can we get the angle of vf?

[@yoprofmatt]

The vector drawing at 5:38 should tell you how to calculate the final angle for vf. Cheers, Dr. A

[@KumarHemjeet]

I am gonna marry that girl who answered -9.81.

[@yoprofmatt]

Better master your physics then! Cheers, Dr. A

[@vav5838]

wait how are you writing backwards what the heck

[@user-nh2ju1se3z]

Благодарю

[@glorymanheretosleep]

Did you ever do a how far it hit the ground?

[@yoprofmatt]

glorymanheretosleep, Not sure if I did. Seems like I must have done that somewhere. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@Marranrageh]

There is the biggest mistake that the professor made which Vi is equal 20 and it is not 30

[@kkkkk393]

🌹

[@maxamedwalixasan6035]

When Vf=√Vi²+2gh why Vi²=30 Because gives angle is 30 tell me Proffesior

[@ritikrajgupta4828]

No it's wrong because sin30= 1/2 so Vi2= (20×1/2)2 = 100

[@weeborghini4016]

I guess we could also use energy to solve this questoon (mgh and KE)

[@yoprofmatt]

Absolutely. You're looking ahead. Cheers, Dr. A

[@johanart5423]

please tell me what your software sir .... tell me

[@yoprofmatt]

www.learning.glass

[@adrianchaix4733]

would this still work with h=0?

[@yoprofmatt]

Adrian Chaix, Yes of course. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@moiralewis3117]

saved my life #considerthisvidliked

[@trookie2179]

Shut that damn bird up!!!

[@sreetejkalapatapu8291]

initial velocity was 20 not 30

[@yoprofmatt]

Yep. Thanks for paying attention. Cheers, Dr. A

[@sahildharme3138]

Sir can you plz explain v-t,a-t,s-t,a-s V-s graphs

[@yoprofmatt]

Here you go: kzbin.info/www/bejne/qZbRnoyno7SMsJo Cheers, Dr. A

[@sagarkadam8048]

I saw complete video just to know how you write in reverse direction

[@yoprofmatt]

sagar kadam, Not writing backwards (I'm not that talented). The board is called Learning Glass. You can check it out at www.learning.glass Cheers, Dr. A

[@clifmsingi8119]

I don' understand anything

[@Loots1]

i got vf =35.68 m/s and t= 4.2s

[@zeusjanseng.lujares7428]

Oh god the squeak on that board is irritating.

[@yoprofmatt]

Imagine standing right next to it. Awful. Cheers, Dr. A

[@ichirosuzuki9368]

man, you are so handsome

[@sumaiyaesry2250]

i dont get ittt

[@yoprofmatt]

What don't you get? Perhaps I can help. Cheers, Dr. A

[@sumaiyaesry2250]

I finished my PHY exam.. Thanks anyway ... + I LOVE YOUR VOICE

[@hno.s]

سبوره شفافه والا شنو 😂

[@yoprofmatt]

I don't think Google translate worked properly for this comment, but thanks anyway. Cheers, Dr. A

[@user-zh6pd6co5o]

اخيرا مصري

[@elon8595]

2:52 sir a planet with a name earth has acceleration due to gravity 9.8m/s^2

[@parvizscott]

Nitin Nitin Dude, The acceleration in X-axis is zero on earth The gravity is pull us back only in y-axis It would be crazy if it's pull us forward hahaha

[@elon8595]

Don'tTellDon'tSeeOfficial 😅

[@elon8595]

Don'tTellDon'tSeeOfficial thanks

[@parvizscott]

But Physics is so hard for me anyway 😂