AS Physics moment question
So this is the question I got in test today.
Basically that circle thing on my best drawing is pulley. The first question was show that the mass of the beam is 3.5kg and I did it.
Then next question was a new mass M was added to the beam at 0.4m away from the left end of the beam (it said it was A but forgot to put it on my drawing lol) and find the maximum possible value of M to make it equilibrium (pulley can move)
I thought that the maximum possible vertical component of the tension is 2*9.81 because the pulley can only go down to 0 degrees and this gives Cos0 which is 1, and this gives largest vertical component of the tension. Right?
So the moment clockwise is the 2*9.81*1.6m which is the perpendicular distance from P the pivot.
Then I thought that must equal to the anticlockwise moment caused by the weight of the uniform ruler and the new weight. Since it's uniform, I did the weight of ruler times 0.8m, plus 1.2M.
The sum I thought was equal to the moment clockwise with the tension, so I made it an equation and tried to solve it. But then it gives me NEGATIVE VALUE. Is that even possible?
Heeeelp
Posted from TSR Mobile
Basically that circle thing on my best drawing is pulley. The first question was show that the mass of the beam is 3.5kg and I did it.
Then next question was a new mass M was added to the beam at 0.4m away from the left end of the beam (it said it was A but forgot to put it on my drawing lol) and find the maximum possible value of M to make it equilibrium (pulley can move)
I thought that the maximum possible vertical component of the tension is 2*9.81 because the pulley can only go down to 0 degrees and this gives Cos0 which is 1, and this gives largest vertical component of the tension. Right?
So the moment clockwise is the 2*9.81*1.6m which is the perpendicular distance from P the pivot.
Then I thought that must equal to the anticlockwise moment caused by the weight of the uniform ruler and the new weight. Since it's uniform, I did the weight of ruler times 0.8m, plus 1.2M.
The sum I thought was equal to the moment clockwise with the tension, so I made it an equation and tried to solve it. But then it gives me NEGATIVE VALUE. Is that even possible?
Heeeelp
Posted from TSR Mobile
With your current diagram, even if M=0, the beam still rotates counter clockwise. Are you sure your value of 3.5kg is correct?
Also, am I correct in saying that the 30 degrees written down was for the purposes of finding 3.5, and the question is: if you can move the pulley to any position, what is the maximum value of M possible while still being in equilibrium? If not, I don't fully understand what you are asking. But your current free-body diagram is rotating, and you'd need a clockwise moment (-ve M in your diagram) to correct this.
Also, am I correct in saying that the 30 degrees written down was for the purposes of finding 3.5, and the question is: if you can move the pulley to any position, what is the maximum value of M possible while still being in equilibrium? If not, I don't fully understand what you are asking. But your current free-body diagram is rotating, and you'd need a clockwise moment (-ve M in your diagram) to correct this.
Original post by lerjj
With your current diagram, even if M=0, the beam still rotates counter clockwise. Are you sure your value of 3.5kg is correct?
Also, am I correct in saying that the 30 degrees written down was for the purposes of finding 3.5, and the question is: if you can move the pulley to any position, what is the maximum value of M possible while still being in equilibrium? If not, I don't fully understand what you are asking. But your current free-body diagram is rotating, and you'd need a clockwise moment (-ve M in your diagram) to correct this.
Also, am I correct in saying that the 30 degrees written down was for the purposes of finding 3.5, and the question is: if you can move the pulley to any position, what is the maximum value of M possible while still being in equilibrium? If not, I don't fully understand what you are asking. But your current free-body diagram is rotating, and you'd need a clockwise moment (-ve M in your diagram) to correct this.
Yes 30 was to confirm that the mass of the beam is 3.5kg
And you can move the pulley in next question
It's from my memory - maybe it was 2.5kg?? It was around that number
pretty sure it was 3.5 though Maybe the teacher messed up when making test because in the very first question it asked me to find T1 and T2 yet in answer box it said T1 and T1 lol
Edit: yes it was 3.5kg definitely - asked my friend...wth. how did the first question even work then!?
And is it even possible to be asked for negative mass????
Posted from TSR Mobile
(edited 9 years ago)
Original post by C0balt
Yes 30 was to confirm that the mass of the beam is 3.5kg
And you can move the pulley in next question
It's from my memory - maybe it was 2.5kg?? It was around that number pretty sure it was 3.5 though
Maybe the teacher messed up when making test because in the very first question it asked me to find T1 and T2 yet in answer box it said T1 and T1 lol
Edit: yes it was 3.5kg definitely - asked my friend...wth. how did the first question even work then!?
And is it even possible to be asked for negative mass????
Posted from TSR Mobile
And you can move the pulley in next question
It's from my memory - maybe it was 2.5kg?? It was around that number
pretty sure it was 3.5 though Maybe the teacher messed up when making test because in the very first question it asked me to find T1 and T2 yet in answer box it said T1 and T1 lol
Edit: yes it was 3.5kg definitely - asked my friend...wth. how did the first question even work then!?
And is it even possible to be asked for negative mass????
Posted from TSR Mobile
Negative mass does not make sense, no. Negative force would but I don't think the question looks like it's asking for a force TBH.
Original post by lerjj
Negative mass does not make sense, no. Negative force would but I don't think the question looks like it's asking for a force TBH.
I know! I was like oh wait, it might be asking for force (force is a vector so got direction, right?) so I read the question like 3 times and it clearly said mass.
I don't think anyone's done it - except one person who got like 0.3 something but it obviously isn't possible as I'm confident in my method and I trust you for saying you need -ve mass!
Posted from TSR Mobile
(edited 9 years ago)
Quick Reply
Related discussions
- GCSE Exam Discussions 2024
- Physical
- Maths moments question
- Advice for applying for physics undergrad
- physics a level
- Mechanics moments in equilibrium
- revision
- A Level Maths Moments question
- Why is tension not equal to weight in moments questions?
- Physics - i need a miracle
- Urgent Isaac physics help !!
- Physics question moments
- Edexcel A Level Physics Paper 1: Advanced Physics I 9PH0 01 - 24 May 2023 [Exam Chat]
- Physical
- physics during gap year help!!
- Engineering A levels vs Btec
- Mathematics Of Mechanics (yay)
- A-level Further Maths Study Group 2023-2024
- AS physics
- Need help on deciding a major, Physics or EEE?
