Physics 8 Work, Energy, and Power (33 of 37) Variable Friction - Example 2

In this video I will find x(final)=? of a 2.0kg block sliding down an arc with a variable coefficient of friction relative to the angle of the arc.

Next video in this series can be seen at:

[leekoller]

Aren't you neglecting the contribution to the normal force due to centripetal acceleration,
mv^2/R

[aniket_Kumar]

Sir, normal force here depends not only on angle but also on velocity, due to centripetal force . And problem here is, I can't just add mv²/R to mgcosθ because "v" at that point depends upon how much potential energy is lost in form of heat which is unknown.
Please give me the solution sir .
Thank you.

[hellothere]

profesor I just wanted to tell you thank you for these videos you have taught me more then the profesors at my university about physics and math (I wish I was joking but its the truth) I am almost 100% sure the only reason I will pass my midterm and finals about phyisics (callculus is a difrent story XD) its because of your videos without them I would have failed miserbly so honestly from the bottom of my heart and I say this for everyone who has a bad profesor thank you in 3 days my finals are coming but how much i know now and how much i knew back then is a lot to say the least thank you stay safe profesor


Update: I got a 90 on my finals lesss goo

[tamaraandalexischristodoul]

Lovely video, thank you. I'm actually confused by some of the comments and your answers relating to centripetal force. You say that you've ignored it for simplicity. But isn't the centripetal force just effectively the resultant force towards the centre of the circular motion? i.e. here, centripetal F = N - mg cos (theta). And then N - mg cos(theta) = mv(squared)/r
The centripetal force isn't 'another force' that can be added or ignored, it is the net effect of the forces that have components towards the centre of the circle, no? A bit like a 'resultant force' isn't another force, but the net effect of other forces. Please correct me if wrong.

[umiturgutaswwsa]

I didnt understand that why we say Rdtheta ?Does it have any relationship with circular motion like circumference formula?

[rajaryan]

Solution might be wrong as circular motion of the particle is not considered, , due to circular motion Normal is different than mg cos(theta), , please give explanation.

[anayetnayeem]

i am being confused when i integrate the work done against friction 0 degree to 180/360 degree. ( for a half or full loop)

the result showing that the work done against friction is zero, but how can that be?
my question is, what will be the result if i integrate like this video, 0 degree to 180 degree for a half loop?

[fizixx]

Great problem....the calc is so good to see! :)

[solracevol]

The way you figured out the components of theta was different than your previous video of Conservation of Energy (9 of 11) sliding in a bowl.  In that one the parallel component was mgcos(theta) and in this one it is mgsin(theta).  Also the normal force was mgsin(theta) on the other video and this one it is mgcos(theta).  Am I missing something?  Is there a difference in application between sliding in a bowl and sliding down a quarter circle with the same coefficient of friction?   Thank you, love your videos.

[albertolemosduran]

It is missing the centripetal force and the friction force depends on the velocity of the block...

[wrenchesinthegears]

Hi. I am wondering if this is correct.?
For the Normal force you have said it is equal to mgcos(theta), nhowever since the block is in circular motion, shouldnt you also consider the Normal acceleration of the block.
So the Sum of the forces in the Normal direction:
N -mgcos(theta) = m(an) therefore. N = mgcos(theta) + m(an)

I am stuck on a question like this and cannot work out how to solve it. Your method is solvable, but it doesnt consider the normal acceleration, which will affect the friction force and hence the work done by friction.

[qiyuanyap]

sorry sir i dont understand about cos theta qual to the angle between angle of motion and angle of friction

[boboganbobogan]

is normal force always equal to mgcos theta in this example? because if an object moves in a circular trajectory there must be centripetal acceleration, which in this case comes out to be zero? is not it true that normal force has to be larger than mgcos(theta) in order for centripetal acceleration?

[perinjhaveri]

Sir, I have some doubts.
1) Wouldn't the integration of cos(theta) be -sin(theta) instead of +sin(theta)?
2) In what situations do we have to take the final KE as 0? For eg. in this video, you considered it but in some of them, you just say that final KE is zero.
3) Is there any way to calculate work done to oppose the friction in a circulate path, (like in this video), if you've been given *mass=1kg, R=5m, Initial angle with tangent (90) and final angle with tangent (127 from initial or 37 from 0), FRICTIONAL COEFFICIENT NOT GIVEN.
Options (just in case):
a) 80 J
b) 40 J
c) 20 J
d) 60 J


Your videos have been of great help!

[AmarKumar-zuwh]

How can you neglect the centripetal acceleration.It will change the normal to mgcos(theta)+mv²/R and then will get problem in integration as v is a function and not a constant.

[jetjet]

why is the normal force, mgcostheta? shouldnt it be mgsintheta? PLEASE REPLY SIR

[amanchaure]

sir u have taken d theta in the anticlockwise direction!
but at the same time u have put the limits 90degree to 0 degree in (sin theta)
sir the radius 10 is rotating in anticlockwise direction so the limits must be 0 to 90 degree to
(sin theta) ..m i right ??if not pls xxplain me how????

[IshitaKukreti]

sir,
the body is undergoing circular motion in that particular segment. won't a centripetal force act on it?
also will the motion then be uniform circular motion or non uniform?
what would be the direction of friction in such a case?

[arbaazzkhann]

THANK YOU FOR THAT WOTRHY CONTENT REALLY HELPFULL...
BUT KINDLY TELL ME WHY YOU DON'T CONSIDER CENTRIFUGAL FORCE... I AM STUCK IN IT

[junitandra]

I'm just slightly confused. You have so many videos (which I seriously like) but they're also scattered into different playlists. For instance, this video should be related to conservation of energy yet it's has its own playlist. But what I'd like to say is, I'd really like if you could recommend me what videos I should watch for preperation of college level mechanical engineering and dynamics. I find more related topics in your phyiscs and mechanics videos than on your mechanical engineering playlist. Maybe because you're already a step ahead in mechanics than what we read in my country. Hope you read this.