Conservative principles

two particles of mass m and 2m are connected by rigid rod(mass≈0) and slide with μ=0 on circular path. of radius r inside of vertical circular ring.If system released at rest at θ=0°.
Determine
1)velocity v of particles when rod passes horz.position
2)max velocity of particles
3)max value of θ

18 Answers

62
Lokesh Verma ·

oh not the one u said..

we dont need to find the potential energy after finding the CM..

you can do it by taking summation of mgH

24
eureka123 ·

Answer is v2=gr(3-2√2/3√2)

plzzzz explain ""finally it will be 3mgr(1-1/√2)""

i am having confusion in soln becoz i am used to solve questions by first solving COM

62
Lokesh Verma ·

I edited my answer..

i think that should do..

if not i think i must be making some blunder which i am not able to see

24
eureka123 ·

what happened to my question?

24
eureka123 ·

ok i agree with u....It will be easy for 2 or atmost 3 particles......But when particles increase should we follow CM method????

62
Lokesh Verma ·

almost always the one without finding the CM

24
eureka123 ·

which method is easier to adopt during exam????

62
Lokesh Verma ·

well eureka that is not always necessary.. you can do without doing what u are saying :)

24
eureka123 ·

But sir when a system of particles is there ,,, dont we first find CM and then proceed with Potential energy calculations????

62
Lokesh Verma ·

This i think you can do by simple work energy theoerm

Conservation of energy (PE+KE)

I dont think this is tough..

this only looks tough.. (Or else i am raelly missing something)

Eureka.. YOu have solved much tougher questions than this one..

give it a shot once... or else just tell me i will give the full soln :)

62
Lokesh Verma ·

oops yes small mistake.. will fix that :)

24
eureka123 ·

sir howz initial potential energy 2mgr ?????????? Dont u think we first have to locate CM coordinates at t=0 and then get potential energy......

And then again when rod is horz?????

24
eureka123 ·

nops....

62
Lokesh Verma ·

second part..

Potential energy will be

2mgr(1-sinθ) + mgr(1-cosθ)

mgr(3-2sinθ-cosθ)

For kinetic energy to be max this has to be min...

so for min potential , 2sinθ+cosθ has to be max = √5

min potential will be mgr(3-√5)

Initially it is 2mgr

Change is mgr(√5-1)

This is equal to 1/2 (m+2m) v2

62
Lokesh Verma ·

haha.. ok :)

initially the potential energy is 2mgr
finally it will be 3mgr(1-1/√2)

both will have the same "speed"

So that will be

1/2(m+2m)v2=2mgr-3(1-1/√2)mgr

3/2 mv2=mgr(2-3+3/√2)
3/2 mv2=mgr(-1+3/√2)
v2=gr(√2-2/3)

Is this correct?

24
eureka123 ·

Oh my GOD..........I missed something in figure........
here is the correct one

This came to light when I read this"" initially the potential energy is 2mgr""

24
eureka123 ·

helpppppp

24
eureka123 ·

Sir I solved this type of question when masses were equal....In that case when rod became hrz angles made were 45°....I am not sure about the situation here........(Becoz we certainly need the position of COM)..............Plz help

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