Physics: Post your doubts here!

[nehaoscar]

Someone explain this please
the grade thresholds say that the maximum mark is 260 and 130
but then the components add up to 270 and 140 ...
Why do they say it as 260 and 130 then???

 

[ahmedish]

View attachment 57272
Someone explain this please
the grade thresholds say that the maximum mark is 260 and 130
but then the components add up to 270 and 140 ...
Why do they say it as 260 and 130 then???

the practical paper is ratio'd down to 30, so if you get 32/40 in practical, your grade is counted as 24/30

 

[nehaoscar]

the practical paper is ratio'd down to 30, so if you get 32/40 in practical, your grade is counted as 24/30

Ohh ... do you know why they do that?

 

[ahmedish]

Ohh ... do you know why they do that?

I'd guess because practical isn't as important so they picked that, they do it in other subjects as well, even gcses.

 

[nehaoscar]

Ok so the part c is the question
now the mark scheme says:

Now if centripetal force is greater shouldn't the mud be held on the disk?
Is it a typo... should it be centrifugal instead?

 

[nehaoscar]

I'd guess because practical isn't as important so they picked that, they do it in other subjects as well, even gcses.

Oh ok They should just keep it as 40 or make the actual paper out of 30 Haha idk why i don't like this

 

[nehaoscar]

i think you should forget about centrifugal.
don't think it's even in the syllabus.

Yeah it's not in the syllabus but centripetal force keeps an object in circular motion, so if it's greater, the object shouldn't fly off but would be kept in motion right?

 

[ahmedish]

Can someone give me an ideal answer to give in
http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s15_qp_22.pdf
4bi ( kinetic model) and here http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s13_qp_21.pdf 4b
(same question) please urgent my exam is tomorrow

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s14_ms_22.pdf
why cant i say interfere in 7a

someone answer these please

 

[nehaoscar]

they are different bodies, so the mud would fly off.

I'm sorry but I don't get it
So here's what I think ... please correct me wherever possible
1. The mud is placed on the disc when the disc is stationary
2. The disc starts to move with an increasing angular velocity w (omega)
3. The centripetal force keeps the mud on the disc so it doesn't fly off
4. At the edges the centripetal force is greater than at the center
So I hope these 4 points are correct
Then the centripetal force holds the mud in place so it doesn't fly off right? ...
So if this force is greater, why will the mud fly off when it's role is to hold it in place?

 

[nehaoscar]

Can someone give me an ideal answer to give in
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s15_qp_22.pdf
4bi ( kinetic model) and here http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_21.pdf 4b
(same question) please urgent my exam is tomorrow

The molecules of the gas are in random motion and are constantly colliding with each other and the walls of the container
When they collide with the walls of the container, there is a change in momentum
The force (pressure) exerted by the molecules is equal to the rate of change of momentum
The average force (pressure) is the sum of all the individual collisions of the molecules with the walls of the container

 

[nehaoscar]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s14_ms_22.pdf
why cant i say interfere in 7a

I guess because the question asks about interference so you can't use that word in the answer

 

[The Sarcastic Retard]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s15_qp_22.pdf
Q2 and Q4

 

[awesomaholic101]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s15_qp_22.pdf
Q2 and Q4

U want soln?
Q4a:

Other subquestions in ms

 

[The Sarcastic Retard]

U want soln?
Q4a:

Other subquestions in ms

Oh sorry, I forgot to mention the subparts of the question. I got this.. I dont know how to write for b and c.

 

[Farheen1201]

I'm sorry but I don't get it
So here's what I think ... please correct me wherever possible
1. The mud is placed on the disc when the disc is stationary
2. The disc starts to move with an increasing angular velocity w (omega)
3. The centripetal force keeps the mud on the disc so it doesn't fly off
4. At the edges the centripetal force is greater than at the center
So I hope these 4 points are correct
Then the centripetal force holds the mud in place so it doesn't fly off right? ...
So if this force is greater, why will the mud fly off when it's role is to hold it in place?

The centripetal force increases with increasing radii. The mud on the edge is the farthest away ergo maximum radii. Hence it experiences greatest force and flies of first. The mud on the disc will also fly off but after the mud on the edge has flown off.

 

[nehaoscar]

teh centripetal does not keep the mud on the disc.

a 'centripetal' force is any force that acts towards the centre. since the mud is on an object in circular motion, it will experience a force.

well, just imagine the real case scenario, the mud would definitely get thrown off.

if anyone else can provide a clearer explanation, you are welcome.

Ok yeah taking the real case scenario it is clear
But then as you said "a 'centripetal' force is any force that acts towards the centre. since the mud is on an object in circular motion, it will experience a force."
Doesn't that mean the mud will experience a force towards the centre?

 

[nehaoscar]

The centripetal force increases with increasing radii. The mud on the edge is the farthest away ergo maximum radii. Hence it experiences greatest force and flies of first. The mud on the disc will also fly off but after the mud on the edge has flown off.

Ok... but is the force the mud experiences the centripetal force?

 

[Farheen1201]

Ok... but is the force the mud experiences the centripetal force?

Yep

 

[nehaoscar]

Yep

Ok so then if the mud experiences a centripetal force, isn't the direction of this force towards the center of the disc?
So then the mud would move towards the center and not fly off right?

 

[JamesWhite]

Hi there!

Can anyone explain this question from paper 11 summer of 2015 for me?

A conveyor belt is driven at velocity v by a motor. Sand drops vertically on to the belt at a rate of m kg s^( –1) .
What is the additional power needed to keep the conveyor belt moving at a steady speed when the sand starts to fall on it?
A 0.5mv B mv C 0.5mv^2 D mv ^2

the answer is D.