find min friction

Two bodies of mass m and 4m are attached with string.Body of mass m length l(String) is executing oscillation of amplitude θ while other is at rest.The min coeff of friction between 4m and ground should be.....

15 Answers

33
Abhishek Priyam ·

Find max tension in the string first...

24
eureka123 ·

max tension will be at amplitude naa ??????

33
Abhishek Priyam ·

T=mv2/l+mg.cosα

write v in terms of α and then differentiate it to find α for max T and then that max T will help U further..

:)

33
Abhishek Priyam ·

Should i post complete soln... ??

In b/w u r in which class??

24
eureka123 ·

wait a second doing it..............i am in 12th........

33
Abhishek Priyam ·

okie..

i asked bcause ur profile show below X :P

24
eureka123 ·

but why are we differentiating ?????Why is T not max at amplitude of oscillation?

And about my class I will correct it very soon........

33
Abhishek Priyam ·

bcause T depends on two things v2 and cos(angle) so if u say at amplitude it is max but how v=0 then and cos() is also small..

well a wild guess it should be at mean position bcause there v is also max and cos() is aslo max i.e. 1

so try with mean position..

24
eureka123 ·

ooops sorryy......didnt think about that......ok tryng .........have u reached the answer????

33
Abhishek Priyam ·

[3] not solving it just seeing and replying..

actually i am downloading something so in between that am having a peep here

[3]

But if u want i can solve it..

24
eureka123 ·

okkk solve it.....maybe i am making mistake while diff........i am getting absurd answer.

33
Abhishek Priyam ·

okie .......

:)

33
Abhishek Priyam ·

is μ=(3-2cosθ)/4

or else i am feeling sleepy [7]

24
eureka123 ·

no u arent sleepy........maybe i am sleepy thats why i am making mistakes.....give ur soln ......

33
Abhishek Priyam ·

T is max at lowest point as i explained above:
it should be at mean position bcause there v is also max and cos() is aslo max i.e. 1

so by writing energy conservations mgl(1-cosθ)=mv2/2

we get mv2=2mgl(1-cosθ)

so as T=mv2/l+mg.cosα...............(α=0 as lowest point)

there fore T=mg(3-2cosθ)

and T=μmin4mg

hence the answer..

:)

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