Welcome back students so students you're talking about friction problems let's continue with few more examples now in this give an example we have two blocks A and B there's a force of 120 Newtons which is acting on the left of a and a force of 100 Newtons ’s which is acting on the right of B the coefficient of friction in the A end surfaces 0.9 and coefficient of friction between B end surfaces 0.3 mass of a is 10kg and mass of B is 20 kg now it is given that we have to find the tension in the string in this particular scenario that does this ,this situation is given we have to find tension now students this particular Scenario that is a very beautiful situation where it will be teach us many Things now what all possibilities can arise now as a result of these two forces when 120 and 100 the possibilities that can arise are, a and B move and a and b don't move now for any possibility what we need to know is what exactly will be d limiting value of frictions because in this case Newest meu k are not mention separately will take meu s and meu K to be seen and if the friction and static we need meu n and if the friction is kinetic then again we need meu n in so basically first thing is to know what exactly will be the limiting value our meu times n now for a since mass of a is 10 therefore mg will be hundred and meu between a surfaces 0.9 therefore a max will be 90 similarly FB max is 60 so the thing is if both a and B move in friction will be kinetic and the values of kinetic friction will be nineteen sixty and it worked in we don't move then whatever the value of friction will be that value of friction should be less than nineteen sixty pretty simple now let us assume in first place assume that both bodies move well both bodies move then it is pretty clear that 120 minus hundred that is 120 left and hundred right so 120 minus hundred is the driving force which is trying to drive a and b the words left now when 120 minus 100 that is 20 is driving in with words left friction on both a and B will act right and it will oppose the motion since a and b move friction will be kinetic the values are nineteen sixty therefore the opposing force are the resisting force will be meuA into na plus meuB*nb that is little be 150 newtons 120 newtons and were acting opposite I think are present there for the inside 120 minus hundred is the driving force friction will be opposing force with friction oppose this motion relative motion kinetic friction opposes of relative motion so over here what we can see you can see that since resisting force is greater than driving force their for how can motion happen therefore this case is not possible we can conclude that's a system remain stationary did it not move our assumption was incorrect right students so now when this assumption is incorrect that both a and be moved what is the next possibility A and B don't move when the A and B don't move in bad as well there can be two possibilities which one possibility will be that friction will be static for both a and B when I says that direction I mean to say friction will be less than limiting friction for both a and B this will be possibility one second possibility will be the frictional will be static for one and limiting for another
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