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# Unit 4 Physics Edexcel A2 and Edexcel IAL Watch

1. Can someone help me with this question from jan 2013 question 13 c2

Ive got A and C mixed around and i have no idea how what ive done is wrong, someone explain?
2. (Original post by AndyOC)
Can someone help me with this question from jan 2013 question 13 c2

Ive got A and C mixed around and i have no idea how what ive done is wrong, someone explain?
The centripetal force is the resultant force of the weight + contact (reaction) force, which causes the cabin to accelerate. It thus always acts towards the centre of the circle.
At A: Centripetal force = mg - r
The weight must be greater than the reaction force in order to provide a centripetal force, hence the reaction force is at a minimun.
At C: Centripetal force = r - mg
Here, the reaction force must be greater than the weight, hence the reaction force is at a maximum.

Hope that helps
3. (Original post by candycake)
The centripetal force is the resultant force of the weight + contact (reaction) force, which causes the cabin to accelerate. It thus always acts towards the centre of the circle.
At A: Centripetal force = mg - r
The weight must be greater than the reaction force in order to provide a centripetal force, hence the reaction force is at a minimun.
At C: Centripetal force = r - mg
Here, the reaction force must be greater than the weight, hence the reaction force is at a maximum.

Hope that helps
Brilliant thank you!
4. (Original post by candycake)
English lit - the course looks great and really versatile! Did you apply for maths?
I did apply for maths, for the same reasons that you chose English Lit
5. Sorry for asking so many questions. I've got two more more
1. I don't understand why the force on the rod acts upwards and not downwards.
2. Why do you need to add the mass of the stationary positron to find the total energy of the system? ie why is it 1.58+0.511+0.511 instead of just 1.58+0.511?

6. This is the reason why Physics A level is the biggest ******** & a scam.

Never in my physics class did we disect a cable to find more than one wire and never did anybody tell me anywhere, no revision guide or revision video, that cables have wire's going in different directions. That's almost half a grade in a question where you literally have to either have electrician experience or you get no marks!!!

**** edexcel!
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7. (Original post by target21859)
Sorry for asking so many questions. I've got two more more
1. I don't understand why the force on the rod acts upwards and not downwards.
2. Why do you need to add the mass of the stationary positron to find the total energy of the system? ie why is it 1.58+0.511+0.511 instead of just 1.58+0.511?
As far as I'm aware:
1) I think the force on the wire is up, but by N3 the force on the magnet is down.
2) You have to add the mass to calculate the total mass-energy since the energy provided is KE only
8. (Original post by candycake)
As far as I'm aware:
1) I think the force on the wire is up, but by N3 the force on the magnet is down.
2) You have to add the mass to calculate the total mass-energy since the energy provided is KE only
What do you mean by the force on the magnet is down?
9. I don't suppose anyone has a list of definitions (e.g. uniform electric field, magnetic field etc) they would mind sharing please? Usually the text books have glossaries but I can't find a list of definitions anywhere

Thanks, I would be so grateful for any help
10. (Original post by target21859)
What do you mean by the force on the magnet is down?
According to N3: If object A exerts a force on object B, then B exerts a force equal in size and opposite in direction on A.

Therefore, there is an equal and opposite force acting on the magnet (from the rod) which, in this case, acts downwards
11. Does anyone know how to derive I = (delta V / delta t ) x C
12. Hey, can anyone explain this to me? Apparently the answer is like a sin wave but with the two pulses separated by a small region at 0 V. I don't really get how it's that.
13. (Original post by ayvaak)
Does anyone know how to derive I = (delta V / delta t ) x C
Surely it's that Q = CV, so C*dV/dt is dQ/dt which is I?
14. Does anybody know wether the all answers should be to 3 sgf or does depend on the data ?? If so, Please elaborate. Thanks !!
15. (Original post by omar5478)
Does anybody know wether the all answers should be to 3 sgf or does depend on the data ?? If so, Please elaborate. Thanks !!
All answers can be up to one significant figure more than the data provided but cannot be less. I always do it to 3 s.f. just in case
16. (Original post by Inges)

This is the reason why Physics A level is the biggest ******** & a scam.

Never in my physics class did we disect a cable to find more than one wire and never did anybody tell me anywhere, no revision guide or revision video, that cables have wire's going in different directions. That's almost half a grade in a question where you literally have to either have electrician experience or you get no marks!!!

**** edexcel!
I think this relies on GCSE physics knowledge (remember the Earth wire, live wire and neutral wire?). It's a sh**** move because people definitely wouldn't remember that (I wouldn't have under exam conditions)
17. (Original post by PhysicsIP2016)
All answers can be up to one significant figure more than the data provided but cannot be less. I always do it to 3 s.f. just in case

Does anyone by chance know the difference between induced emf and induced current? Do they act in the same direction
18. (Original post by ayvaak)
Does anyone by chance know the difference between induced emf and induced current? Do they act in the same direction
The induced current will be in the same direction as the induced emf.
19. (Original post by ayvaak)
Does anyone by chance know the difference between induced emf and induced current? Do they act in the same direction
The induced e.m.f and the induced current do act in the same direction (because they both oppose the change in flux linkage that induces it) however a current will only flow if connected in a circuit
20. (Original post by PhysicsIP2016)
The induced e.m.f and the induced current do act in the same direction (because they both oppose the change in flux linkage that induces it) however a current will only flow if connected in a circuit

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Thank you do you by any chance know why we dont times the answer by sin30?
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