AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread]

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Can anyone explain why racing tracks are bunked in terms of centripetal force.

It reduces the frictional force on the tyres as the horizontal component of weight will provide some of the centripetal force keeping the car on the track. If the ground was flat there would be no horizontal component of weight. :smile:

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This means that you can go around a bend on a banked track quicker than you can when its flat

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(edited 8 years ago)

Reply 2521

sykik

Original post by _Caz_

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This means that you can go around a bend on a banked track quicker than you can when its flat

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When the ground is flat how does frictional force provide centripetal force?

Reply 2522

Absent Agent

Original post by sykik

When the ground is flat how does frictional force provide centripetal force?

Frictional force on the tyres keeping the car in a circular path is the centripetal force

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Reply 2523

sykik

Original post by Mehrdad jafari

Frictional force on the tyres keeping the car in a circular path is the centripetal force

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But isn't centripetal force towards the centre? I donno i am getting confused like how can friction provide centripetal force?

(edited 8 years ago)

Reply 2524

Absent Agent

Original post by sykik

But isn't centripetal force towards the centre? I donno i am getting confused like how can friction provide centripetal force?

No, you're not confused, your question is reasonable. The centripetal force is the force required to keep a body in a circular motion, whether that be the circular motion of the earth around the sun or a car turning a roundabout. A car cannot turn around a circle if there is no friction between the tyres and the road because bodies have the "tendency" to move in a straight line. So a car going around in a circle will need a force keeping it in its path and that force is the frictional force. Of course this force is acting towards the centre of the circle because that's how the frictional force is able to keep the car in a circular path.
In fact if there was no frictional force between the tyres and the road (assuming it had some jet engine to power)and the car was attached by a string to the centre of the circle then the string would do the same job as the friction between the tyres.
Is that quite clear?

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(edited 8 years ago)

Reply 2525

sykik

Thanks it makes a lot more sense now.

Reply 2526

Absent Agent

Original post by sykik

Thanks it makes a lot more sense now.

No worries. I'm happy it helped

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Reply 2527

Absent Agent

Guys, it's very awkward but last night i dreamt that i was doing phys5 paper and the six marker was the proof of the kinetic theory of gas equation. My mind may be subjective this time due to the lots of comments it has seen on here lol

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Reply 2528

gcsestuff

Original post by Mehrdad jafari

I thought this too! But surely that would be to easy for a 6 marker ??

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Reply 2529

Ilovemaths96

Original post by gcsestuff

I thought this too! But surely that would be to easy for a 6 marker ??

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But they've never asked this before, and all of the nuclear stufff has been exhausted. Plus nothing on gases for a while (unless they put in a question about thermal)

Reply 2530

AR_95

So it's either a thermal experiment, or the kinetic theory

Reply 2531

Absent Agent

Original post by gcsestuff

I thought this too! But surely that would be to easy for a 6 marker ??

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Well, not if it it was worth less than six marks. And also the derivation of the equation in the textbook seems quite wrong even though the final equations seems right.

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Reply 2532

noseypo

Original post by AR_95

So it's either a thermal experiment, or the kinetic theory

What thermal experiment could it be?

Reply 2533

getback339

Could someone help me with june 2013 question 1 part c? thanks a lot

Reply 2534

Klaxoii

Does anyone know of any solutions to the multiple choice questions?

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Reply 2535

sykik

Hi can anyone explain what should the angle be between. I came across a multiple choice question where they had given us a wrong angle and we had o workout the right one but i don't understand the angle should be between? Thanks

(edited 8 years ago)

Reply 2536

chughes17

Just read that emf is always induced, but current only if the circuit is complete. Can someone explain this a bit? So if the coil was not all the way round, and had a gap, and you drop a magnet through it, will it take longer than if there is no coil?

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Reply 2537

chughes17

Also, can somebody explain alternators from scratch? Including why it's so important we use AC, just everything that's going on there!

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Reply 2538

sykik

Hi I get why EMF is 20 but i don't get how you workout frequency ?

Reply 2539

Lau14

Original post by chughes17

The reason emf is induced in conductors is that charged particles move when in a magnetic field. emf is the potential difference - so the difference in charges - which you'll get in an incomplete circuit because charge will build up at one end due to movement of electrons. In a complete circuit, the electrons continue moving, so you get a flow of charge - a current.