Center of Mass | Advanced Problem | Maximum Extension in Spring with External Force | Three Methods

In this question Maximum extension in a spring is calculated in case when external force is also acting.
problem is solved using center of mass frame and ground frame both.
total three methods are used.
problem statement:
Two blocks of masses m and 2m are connected with a spring with spring constant k are kept at rest as shown on a smooth horizontal surface. A constant force F starts acting on right block. Find maximum extension in the spring during subsequent motion.

this problem is also given in Irodov with problem number 1.152. Advanced problems Playlist

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[PhysicswithAkashGoyal]

If you have voice issue.... Use headphone/ Earphone 🎧

[Algoner]

Sir iam searching for this topic for a month but today iam very much happy I completed it finally all thanks to u sir....

[nidhitiwari]

2nd and 3 rd method is really amazing .... Although I saw 1st method in HCV example but another two are really amazing....

[manjusakhuja]

i was struggling with this question from a long time.. thank you so much sirr !!

[shivamverma]

Aap kamal ho sir.
Please bless us for jee advance 2020

[parthjayswal]

Thank you sir for wonderful explanation

[Prashant-fhpx]

😀😃😃😁😁 cool 😎😎😎 methods only method 3 stuck in mind initially

[sohansingh]

Sir vel of seperation should be 0 wrt ground frame. But in COM FRAME if it's 0 then won't the values of vel change such that vel of seperation in ground frame does not remain 0?

[dots]

Sir constant external force mei reduced mass apply kar sakte hai kya

[vandanavvv]

Superb sir
Waiting for more advance level questions and concepts

[mamtarani]

Nice explanation keep on uploading such videos

[omkarpathrikar]

Sir in the second method if we write NLM eqn at the instant when max. extension has been achieved then v1 would be directly equal to v2 then why is the answer coming wrong at that instant please clarify.

[violinaza]

sir in the third method..while writing work energy theorem eq..shouldn't the RHS be F(x2-x1)?..since total extension of the spring is x2-x1 and not x2 alone?

[akshayanandtiwari]

thank you. it was in my coaching sheet and I was not able to understand.

[jashujaswanth]

Work done by conservative force is 0, but this happens when intial and final points are equal but here the situation is not like that sir

[vanditseksaria]

sir can we say that the last or the second last step in method 2 is alternate form of work energy theorem

[ASHUTOSHSINGH-bdnf]

Sir please playtist pura kijiye sab chapter ka

[ROCKETSCIENCEYT]

Sir why you didn’t include spring force on individual masses while writing net force on blocks wrt COM ? Please help sir very confused 😢

[sachinyadav]

Sir when will be maximum relative velocity occur

[sohansingh]

Sir at 9:25 why lower limit of rhs has 0, it should be initial extension in spring na?