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?

[natalieschwarz]

His skills with writing equations backward is mind boggling.

[spivak]

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

[justinamaynard]

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.

[manuboker]

Wonderful lecturer that makes physics fun and understandable !!!

[dvnsyaswanth]

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 .

[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

[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.

[chabanemoumani]

Very very nice teaching thank you so math ❤

[Roberto]

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?🤐🇿🇦🙆🏽‍♂️

[sonkemctan]

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

[birenderhooda]

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

[lappelduvide]

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!

[sawineta]

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

[abdullahtarek]

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

[haifasaeed]

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

[murphygreen]

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?

[borisdasgupta]

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.

[ksdnsdkumar]

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

[Rachel-rege]

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

[shahadalmahrazi]

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