Author Topic: physics  (Read 19186 times)

Offline ruby92

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Re: physics
« Reply #45 on: March 26, 2010, 10:32:28 pm »
i meant it is...typo  :P :P too much physics
and its Q6 not 5 part a :)

Offline astarmathsandphysics

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Re: physics
« Reply #46 on: March 26, 2010, 10:44:04 pm »
6a)Y is positively charged since drop must be repelled by Y and attracted by X to remain stationary. The electric force must balance gravity.
Is this the right question? V Simple

Offline ruby92

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Re: physics
« Reply #47 on: March 26, 2010, 10:56:10 pm »
yes thnkx  ;D

Offline halosh92

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Re: physics
« Reply #48 on: March 27, 2010, 06:41:01 am »
electricity question:
1.When a battery in a toy car delivers a current of 0.75A, the p.d across its terminals is 1.3 V. when the car's motion is reversed the current delivered by the battery and the p.d. across its terminals becomes 12A and o.80v respectively.
calculate for the battery
a)the emf
b)the internal resistance

2.physics oct nov 2005 q6 part A(explained in detail)

whats the answer to the first question though????????
everyday we wake up is a miracle, then how do we say miracles dont happen?????

Offline astarmathsandphysics

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Re: physics
« Reply #49 on: March 27, 2010, 07:11:12 am »
I am sure the elctricity question makes no sense.

Offline ruby92

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Re: physics
« Reply #50 on: March 27, 2010, 08:51:58 am »
only out teacher seems to think it does and she gives such questions for the mock 
where we all end up ???

Offline ruby92

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Re: physics
« Reply #51 on: March 27, 2010, 11:14:24 am »
Electricity:
Question:
1. State kirchoff's laws. use the laws to deduce the laws of Ia and Ib as shown in the figure.
The circuit is here:
http://tinypic.com/r/t5j3iu/5

2.the circuit is attached.We need to find I1 I2 and I3

could someone solve these immediately
i have an exam tommorrow  :( :(
« Last Edit: March 27, 2010, 11:42:59 am by ruby92 »

Offline halosh92

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Re: physics
« Reply #52 on: March 27, 2010, 12:24:44 pm »
is this the answer for question 2?

I1= 0.44
I2=0.39
I3=0.834

?????
everyday we wake up is a miracle, then how do we say miracles dont happen?????

Offline astarmathsandphysics

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Re: physics
« Reply #53 on: March 27, 2010, 01:40:15 pm »
When I get home

Offline astarmathsandphysics

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Re: physics
« Reply #54 on: March 27, 2010, 02:21:08 pm »
V2+V3=3
I2=2I3 whe I2 is current in 2 ohm resistor etc  by symmetry
2I2+3I2=3 so I2=3/5A IA=IB=3/5A

Offline ruby92

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Re: physics
« Reply #55 on: March 27, 2010, 02:42:54 pm »
V2+V3=3
I2=2I3 whe I2 is current in 2 ohm resistor etc  by symmetry
2I2+3I2=3 so I2=3/5A IA=IB=3/5A
this is the answer to the first question?

Offline astarmathsandphysics

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Re: physics
« Reply #56 on: March 27, 2010, 02:44:36 pm »
Net voltage around left loop is 1V
V=IR so 1=6I so I=1/6A
similarly I2=1/5 and I3=1/5+1/6 sine the currents are opposed

Offline ruby92

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Re: physics
« Reply #57 on: March 27, 2010, 03:22:44 pm »
this is what i did
in the circuit a third current -Ia-Ib is there
for the first loop going in an anti clockwise direction
2Ia+3(-Ia-Ib)-2=0
2Ia-3Ia-3Ib-2=0.
-1Ia-3Ib-2=0.....(1)
in the second loop.
going anticlockwise
-2Ib-3(-Ia-Ib)+2=0
-2Ib+3Ia+3Ib+2=0
1Ib+3Ia+2=0....(2)

solving simulatneously.....
Ib as -o.5
and Ia by substitution as -0.5

what exactly have i done wrong?

Offline Phosu

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Re: physics
« Reply #58 on: March 27, 2010, 04:30:33 pm »
its weird that i got this rite in the exam, but i cant solve it again,
haha heres how i did it.

Ia + Ib = Ic , heres the basic mistake which you did, which caused the whole thing to go rong.

Ia be a, and Ib be b

2-2a-3Ic=0
2-2b-3Ic=0

any 2 above can be used as equation 1

2-2a-3Ic=2-2b-3Ic

3Ic and 2 will get cancelled
you get an equation -2a+2b=0, this will be used as equation 2

now simultaneously solve
i will use loop a, and split Ic current

2-2a-3(a+b)=0
2-2a-3a+3b=0

1)2-5a+3b=0
2)-2a+2b=0

and voila! :D

Offline ruby92

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Re: physics
« Reply #59 on: March 27, 2010, 04:35:24 pm »
whts d final answer???
and wht have i done wrong??
Reply fast
« Last Edit: March 27, 2010, 04:45:47 pm by ruby92 »