# M1: Post your doubts here!

#### Mstudent

I wanted to start this thread for us to discuss about any doubts in the upcomming m1 exam. best of luck guys!

#### husnain99

I wanted to start this thread for us to discuss about any doubts in the upcomming m1 exam. best of luck guys!
Any tips on vectors ? Plus relative velocity stuff ?

#### Mstudent

Any tips on vectors ? Plus relative velocity stuff ?
Vectors are usually a difficult topic! I kinda relate them with physics, makes them a bit easier!

#### Mstudent

guys could you help me out here! Plz don't judge me cuz I was really good at mechanics BEFORE the exams started, now i FORGOT EVERYTHING , at the end of the exams! ANYONE PLEASE URGENTLY!!!

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#### Mstudent

This one also guys. Only B

#### husnain99

Can someone please explain the concept of limiting equilibrium ?

#### Mstudent

Can someone please explain the concept of limiting equilibrium ?
Limiting equilibrium is when the frictional force on a body is MAXIMUM. Let me give you an example:

Imagine you had your mobile phone on your past paper booklet and the booklet is horizontal. Now tilt the booklet a bit, does it move? NO it doesn't because friction is NOT MAXIMUM and the force of gravity on the mobile phone along the booklet is EQUAL to the frictional force and the mobile is in EQUILIBRIUM (NO RESULTANT FORCE!). Tilt the booklet a bit more, stop JUST before the mobile starts to slide on the booklet, at this point the Frictional force is AT ITS MAXIMUM and is EQUAL to the force of gravity on the mobile along the booklet and its STILL IN EQUILIBRIUM, but it is at the point of sliding along the booklet, the friction is JUST ENOUGH to keep the mobile at equilibrium from sliding down, thus LIMITING EQUILIBRIUM (This is the maximum limit for the friction to prevent the mobile moving!)

Hope this helps.

#### husnain99

Limiting equilibrium is when the frictional force on a body is MAXIMUM. Let me give you an example:

Imagine you had your mobile phone on your past paper booklet and the booklet is horizontal. Now tilt the booklet a bit, does it move? NO it doesn't because friction is NOT MAXIMUM and the force of gravity on the mobile phone along the booklet is EQUAL to the frictional force and the mobile is in EQUILIBRIUM (NO RESULTANT FORCE!). Tilt the booklet a bit more, stop JUST before the mobile starts to slide on the booklet, at this point the Frictional force is AT ITS MAXIMUM and is EQUAL to the force of gravity on the mobile along the booklet and its STILL IN EQUILIBRIUM, but it is at the point of sliding along the booklet, the friction is JUST ENOUGH to keep the mobile at equilibrium from sliding down, thus LIMITING EQUILIBRIUM (This is the maximum limit for the friction to prevent the mobile moving!)

Hope this helps.
Thanks mate! this was helpful

#### Mstudent

Thanks mate! this was helpful
you're welcome anytime

BTW could you plz, help me with my questions above?

#### husnain99

Btw after that , ( I mean when friction force is at its maximum and the mobile is on the point of moving ) will friction force change while the mobile is sliding down ? ( given that the booklet is rough )

#### husnain99

you're welcome anytime

BTW could you plz, help me with my questions above?
I covered vectors like a month back and have to revise again
Can help with pully question ..
would upload the answer ..

#### Mstudent

Btw after that , ( I mean when friction force is at its maximum and the mobile is on the point of moving ) will friction force change while the mobile is sliding down ? ( given that the booklet is rough )
When the frictional force becomes maximum, it stays CONSTANT even if the weight of the mobile along the book (if angle along horizontal) is increased. So to find the maximum in this case, use F=uR

hope that helps

#### Mstudent

Yo, will this be accepted if I write

T - 3g = 3ma
2mg - T = 2ma

#### husnain99

Yo, will this be accepted if I write

T - 3g = 3ma
2mg - T = 2ma

View attachment 62554
I don't think so ..
take overall mass on other side too ..

Cause if you take only 2m on the other side then how A can move upward ?

#### husnain99

This one also guys. Only B
View attachment 62553
In this qs did you get your Part A correct ?
Can u tell me why they're taking F as positive and not negative while making equation of motions ???

Btw part B is repeated concept : use cosine rule that's the easiest method ...

#### Mstudent

In this qs did you get your Part A correct ?
Can u tell me why they're taking F as positive and not negative while making equation of motions ???

Btw part B is repeated concept : use cosine rule that's the easiest method ...
Yeah I did part A and I got it correct. I have an easier method for b). You use 2T Cos(theta/2). My teacher told me about it.But how do you find the angle in this case?

#### Mr.Physics

hey from which paper is this question?
the P and Q particles one

#### Mstudent

hey from which paper is this question?
the P and Q particles one
june 2015

#### husnain99

How the M1 today ?
What was the answer for T in kinematics question ?

#### Mstudent

Al hamdulilah it was good. Last was complicated but I answered it well alhamdulilah. I'm sorry man, I really don't wanna discuss about exams, but I got 9N for T.