Class 11 Physics | Rigid Body Dynamics | #25 Example-10 on Rotational Motion | For JEE & NEET

[@alphaiitd1]

Thanks sir

[@3511kat]

Your solved example has helped me to solve a problem about angular momentum in my assignment. Thank you very much!

[@Rajatkumar-dm5uf]

sir didn't understand why angular momenetum would be conserved about the hinge point ?

[@harsha8412]

torque = force x perpendicular distance from axis of rotation. As distance is zero, torque is zero and L is conserved

[@tinkywinky9099]

Harsha Vardhan no, the force is 0 hence its conserved. as from COM distance to point A is not 0 .

[@HarshitJangra-z5v]

Why force is zero

[@ayushsaxena1164]

Great deal of knowledge !! Appreciated!!!!!😀😀😀🙄🙄

[@tpsicmin]

Thank You Sir😎

[@harsh17_17]

Sir if i do with linear momentum Mu/2=3Mv/2 ,,,,v=u/3 ,,,then v=rw ,,u/3l ???? Aa gya sir plz clear it

[@Mr.Tapori]

Same doubt

[@harrymecwan3426]

what about net force acting on it ... is it zero? if it is, then momentum must also be conserved..

[@shivamverma9447]

Hinge forces are present

[@sanchitmehta7181]

can we use energy conservation here ?

[@JUSTFUN-wm8mf]

Sir if we think this question as like mine modified question ......The rod is moving rotationally and after that the ball strikes so can we use the intital angular momentum as ML^2w0/3 (wo is initial angular speed) because of rod ang. Momentum and the final ang. Momentum as ML^2/3 + ML^2×Lw0/2 (as u=Lw0) ........Sir pls reply.......

[@padhai_karle_bhai]

Did you got your answer?

[@nikhilparikh2554]

Sir in this can't we do by linear momentum conservation ....we get v=u/3 ....and the from v=rw we get w as u/3l....???

[@madihasiddiqui4540]

no, because linear velocities of particles of the rod will be different and also hinge force is present preventing rods linear motion

[@kunalverma6940]

Sir how is angular momentum conserved here since torque should not be zero..the rod should experience a torque

[@rohanphutke4999]

both small mass and rod are considered as system

[@surajkumarbehera]

sir, when will the links to download class notes after fundamental classes will be available ?. for now downloads are not available. I want to solve the problems again after class. and you strictly prohibited to take notes during class.

[@physicsgalaxyworld]

The app PG LIVE on which these videos are streamed is going to be re-launched after which notes will be available...

[@surajkumarbehera]

@@physicsgalaxyworld Sir please tell when will it be relaunched? And when will the test series ( premium features ) will come ?

[@raghavs9241]

Dear sir How initial angular momentum is M/2 u L . and also sir can you clarify about the axis of rotation in this example?

[@physicsgalaxyworld]

You need to first understand the basics of angular momentum as how it is calculated... the linear momentum of moving mass M/2 is Mu/2 and about the hinge of rod which is its AOR the angular momentum will be the product of linear momentum and the perpendicular separation of AOR from the line of motion so it is Mu/2 x L... we suggest you to follow our videos in proper sequence either on our mobile app 'Physics Galaxy' or through our website www.physicsgalaxy.com or our channel playlists... you missed the videos previous to this in sequence thats why you are facing this problem...

[@raghavs9241]

Thank you sir.... Got it now......

[@NikhilKumar-ys9up]

After collision, I considered mass of B and ball together (3M/2). Then it's their final angular momentum about A is (3M/2)(L)(required velocity), as it is in circular motion, and equate it to initial angular momentum. But my answer is different, please tell me where I am wrong sir?

[@NikhilKumar-ys9up]

Gotcha😅

[@shivanshuverma5981]

hello sir! why did u say tht the angular momentum is conserved about point 'A'.?

[@Pepe-jw7xw]

Because if we take from any other point then we have to consider the hinge forces also and that will not result in conservation of momentum

[@padhai_karle_bhai]

@@Pepe-jw7xw but then why in initial momentum we took ball, ball ne to abhi hit bhi nahi kiya...

[@ishan__001]

@@padhai_karle_bhai talking abt system sis

[@padhai_karle_bhai]

@@ishan__001 I'm a brother 😂😂

[@ishan__001]

@@padhai_karle_bhai kitna rank aya brother mujhe dar lg rha h

[@AshokKumar-qi4nr]

Sir, here why can't we conserve linear momentum?

[@aryanpratapsrivastava3757]

Impulsive force acts on it

[@hotscandium6892]

Due to rotational motion the centrifugal force acts and hence net force is not zero but yes torque net is zero

[@deuteriumtritium9700]

Sir, as the rod moves up, won't there be torque due to gravitation force?

[@kartikmessner2868]

during collision we only have to consider impulsive forces..gravity is a non impusive force..thus torque due to it will also be non impulsive..thus we can neglect it.

[@deuteriumtritium9700]

@@kartikmessner2868 Thanks :)

[@stealthinator16]

The better answer is that we need to find angular velocity just after the impact. As the rod remains vertical, gravity will pass through the axis of rotation hence it's torque will be zero.

[@SanjeevSingh-gx7bq]

Sir this question came in 20 July mains paper

[@manojwadhwa1856]

Jee advanced 2020 mai bhi similar ek question tha

[@alexs6284]

where is torque of hinge force ???

[@ASHWING.P]

Aree yarr the axis is taken about the hinge

[@nSackStyles]

Since no external force acts, why can't we solve it using conservation of momentum?

[@next_thing_to_god]

the rod is freking rotating bro

[@divitgoyal5901]

Sir can`t we just conserve linear momentum?And secondly why angular momentum only about point A is conserved and not everywhere?

[@physicsgalaxyworld]

Due to the impulse applied at the hinge linear momentum is not conserved in this case and about A only the torque due to force by impulse is zero so angular momentum can be conserved only about A in this case...

[@divitgoyal5901]

Physics Galaxy why about only A torque due to force by impulse is zero??

[@repudirajasekhar3884]

Sir...plz explain in detail... why angular momentum is conserved only at point A.... explain clearly sir... i have doubts about conservation of ang momentum

[@nayannathani32]

can we think of solving this question using energy conservation?

[@physicsgalaxyworld]

As the particle sticks to the rod after collision, here energy loss will occur due to inelastic collision... so energy cannot be conserved...

[@gigachad6844]

Sir, won't the mass after collision become 3M/2 ?

[@physicsgalaxyworld]

Here we are considering bodies independently...

[@saicharanreddy1053]

particle hit acts force

[@satadhi]

hi! why did u say tht the angular momentum is conserverd about point 'A'. What about the others points ,?

[@physicsgalaxyworld]

Satadhi Halder When ball hits the rod, an impulse is imparted by hinge at A due to which at all other points there will be a torque of this force so angular momentum can only be conserved about point A.

[@Rajatkumar-dm5uf]

but still sir torque would still be created about point of collision as there is force and l bieng teh perpendicular distance ?

[@adarshchaturvedi3498]

Physics Galaxy sir please clarify this point again .. Why impulse is imparted only at hinge point and not other points .

[@physicsgalaxyworld]

Because only at this point any external force due to hinge is present... there is no other point on rod where a force can act...

[@adarshchaturvedi3498]

Sir on this topic (conservation of angular momentum) I have some doubts. Sir when and where can I put it to u ..