A2 Physics Unit 4 and 5 Revision Thread

Original post by Vampire-Love4ever

Do we need to know how to derive Newton's Law of Gravitation?

That can't be derived. It's a law.

Reply 121

Original post by Summerdays

That can't be derived. It's a law.

Thanks.

Reply 122

Smithy-92

Original post by Vampire-Love4ever

Do we need to know how to derive Newton's Law of Gravitation?

Not really "derive" it as such, but I guess know that the force due to gravity was measured & shown to be proportional to Mm and 1/r^2 so a constant was introduced.

Reply 123

Original post by Smithy-92

Not really "derive" it as such, but I guess know that the force due to gravity was measured & shown to be proportional to Mm and 1/r^2 so a constant was introduced.

Thanks alot! :smile:

Reply 124

kp_93

Original post by Rosie2039

Heya!
I noticed there wasn't an A2 GCE Physics Revision thread so I started one :smile:

As you people might know that Unit 4 will be on 21st and Unit 5 will be on 27th.
So I was thinking that we could help each other out, clear some doubts and of course motivate each other :biggrin:

I have January and June 2010 papers with marking schemes so if you want you can ask. :smile:

Good luck everyone and I'll be waiting for your response!

have u got jun 11 paper by any chance :biggrin:

joking but i m stressed about unit 4 and 5 at least i will get a good 6 days before unit 5 but unit 4 magnetism is hard

Reply 125

kp_93

can anyone expalin to me how transformer works and what key terms i need to know i m guessing this time the 6 mark question will be on transformer which i dont know so please help!!! anyone :s-smilie:

Reply 126

Original post by kp_93

can anyone expalin to me how transformer works and what key terms i need to know i m guessing this time the 6 mark question will be on transformer which i dont know so please help!!! anyone :s-smilie:

Transformer effect:

*If the current in a coil changes, then so does the magnetic field produced.
*If the changing magnetic flux links with another coil then there'll be emf induced in that coil.
*The coil in which the current is changing is referred to as the primary. The other coil is called secondary.
*To ensure maximum flux linkage between the two coils they are mounted on soft iron core, which becomes magnetized when current flows in the primary, and flux is channeled to the secondary.

(edited 12 years ago)

Reply 127

Smithy-92

aaarrrgghhhh spoilers! havent learned transformers yet xD

Reply 128

Original post by Smithy-92

aaarrrgghhhh spoilers! havent learned transformers yet xD

Sorry!

Reply 129

nikoriku

can anyone explain these questions to me?

What would the period of rotation of the Earth need to be if objects at the equator were
to appear weightless?
radius of Earth = 6.4 × 106 m

A 4.5 × 10–2 hours
B 1.4 hours
C 24 hours
D 160 hours

A 10 mF capacitor is charged to 10 V and then discharged completely through a small
motor. During the process, the motor lifts a weight of mass 0.10 kg. If 10% of the
energy stored in the capacitor is used to lift the weight, through what approximate
height will the weight be lifted?

A 0.05 m
B 0.10 m
C 0.50 m
D 1.00 m

thanks

(edited 12 years ago)

Reply 130

Rosie2039

OP

Original post by kp_93

have u got jun 11 paper by any chance :biggrin:

joking but i m stressed about unit 4 and 5 at least i will get a good 6 days before unit 5 but unit 4 magnetism is hard

Scroll down on the first page of this thread you'll find the papers there :smile:

Reply 131

Smithy-92

Original post by nikoriku

can anyone explain these questions to me?

What would the period of rotation of the Earth need to be if objects at the equator were
to appear weightless?
radius of Earth = 6.4 × 106 m

A 4.5 × 10–2 hours
B 1.4 hours
C 24 hours
D 160 hours

I'm trying to figure out how to approach this, but can't seem to get there. My current thinking is something along the lines of: Current value of g at equator is 9.8 and to appear weightless, g would be 1? And then use g = v^2/r but getting nowhere. I think I'm missing something..

EDIT: Scrap the g=1 thats stupid xD, Use 9.8 = v^2/r to give v as 7919.6ms-1 speed of rotation and v=2pir/T gives T as 1.4 hours.

Original post by nikoriku

A 10 mF capacitor is charged to 10 V and then discharged completely through a small
motor. During the process, the motor lifts a weight of mass 0.10 kg. If 10% of the
energy stored in the capacitor is used to lift the weight, through what approximate
height will the weight be lifted?

A 0.05 m
B 0.10 m
C 0.50 m
D 1.00 m

Energy discharged from capacitor = 0.5CV^2 = 0.5 x 10 x 10^-3 x 10^2 = 0.5J

10% of this is used by the motor, so 0.05J is the potential energy gained by the weight, mgh = 0.05 gives h = 0.051m

(edited 12 years ago)

Reply 132

gummers