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Physics: Post your doubts here!

Scafalon40

Scafalon40

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Scafalon40 said:
Guys can someone help me with this?

If you have a raw data value like l= 6.0 +/- o.4 and you're asked to calculate l^2 and write down its absolute uncertainty, how do you know what the no of significant figures for the uncertainty should be?
And what about a number like x=750 +/- 20 and you're asked to do the same thing as above, only this time it's ln(x) which you have to calculate.
All I need to know is how many s.f should the uncertainty be quoted to.
Thanks!
Click to expand...
Anyone? ^
 
Dug

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A

asangietalks

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Dug said:
Density = Mass/Volume
Volume = (3.5 x 10^-25)/(9.2 x 10^3)
Let 'x' be the length of a side of the cube. From the diagram, the shortest distance between 2 atoms is 'x'.
Volume of a cube = x^3
x^3 = (3.5 x 10^-25)/(9.2 x 10^3)
x = 3.4 x 10^-10 m
Click to expand...


Thank you so much. 1 more question, why we arent multiply the mass of each atom by the number of atom that shows in the diagram?
 
Dug

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asangietalks said:
Thank you so much. 1 more question, why we arent multiply the mass of each atom by the number of atom that shows in the diagram?
Click to expand...
We are finding the shortest distance between the centres of two adjacent atoms. We have the mass of an atom and the density of the crystal is also provided. Volume of the atom can easily be found and then the length 'x' by using cube-root. 'x' is the same as the length measured between the centres of the two adjacent atoms. The keyword here is adjacent. Try to read the statement carefully and understand it.
 
daredevil

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1357913579 said:
Can anyone please help me in
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s03_qp_1.pdf
number-5
Click to expand...
the answer wud be C (330 m/s) becasue the value is to be written correct to the number of decimal places same as the absolute error that means here it is 3 so we have to remove the decimals from our answer which makes it 328 after rounding off and to bring it in accordance with the absolute error we write 330 m/s. do you get it? if not then ask away any problems u hav :)
 
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asangietalks

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Dug said:
We are finding the shortest distance between the centres of two adjacent atoms. We have the mass of an atom and the density of the crystal is also provided. Volume of the atom can easily be found and then the length 'x' by using cube-root. 'x' is the same as the length measured between the centres of the two adjacent atoms. The keyword here is adjacent. Try to read the statement carefully and understand it.
Click to expand...

oke. thnks anyway.. :D would you help to explain no 6 in the same question paper?
 
Scafalon40

Scafalon40

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Guys can someone help me with this?

If you have a raw data value like l= 6.0 +/- o.4 and you're asked to calculate l^2 and write down its absolute uncertainty, how do you know what the no of significant figures for the uncertainty should be?
And what about a number like x=750 +/- 20 and you're asked to do the same thing as above, only this time it's ln(x) which you have to calculate.
All I need to know is how many s.f should the uncertainty be quoted to.
Thanks!
 
daredevil

daredevil

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Scafalon40 said:
Guys can someone help me with this?

If you have a raw data value like l= 6.0 +/- o.4 and you're asked to calculate l^2 and write down its absolute uncertainty, how do you know what the no of significant figures for the uncertainty should be?
And what about a number like x=750 +/- 20 and you're asked to do the same thing as above, only this time it's ln(x) which you have to calculate.
All I need to know is how many s.f should the uncertainty be quoted to.
Thanks!
Click to expand...
your absolute error should be correct to 1s.f. and then the value should be correct to the same no. od d.p. as ur resulting absolute error is.
like if u hav calculated a length to be 20.324 +/- 0.346cm

then ur correct absolute error should be +/- 0.3
and thus the resulting value should be 20.3 as the absolute error comes to 1 d.p.


for another case you have the speed to be 326.55 +/- 1 m/s
then ur answer should be:

327 m/s
because the absolute errror is correct to 0 s.f.

even if the value does not have a number after the decimal but the absolute error is correct to 1 d.p. or so u write abc.0 insead of just writing abc

hope u get it :)
1357913579 u might wanna check this out ... maybe it will help :) ^_^
 
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1357913579

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daredevil said:
your absolute error should be correct to 1s.f. and then the value should be correct to the same no. od d.p. as ur resulting absolute error is.
like if u hav calculated a length to be 20.324 +/- 0.346cm

then ur correct absolute error should be +/- 0.3
and thus the resulting value should be 20.3 as the absolute error comes to 1 d.p.


for another case you have the speed to be 326.55 +/- 1 m/s
then ur answer should be:

327 m/s
because the absolute errror is correct to 0 s.f.

even if the value does not have a number after the decimal but the absolute error is correct to 1 d.p. or so u write abc.0 insead of just writing abc

hope u get it :)
1357913579 u might wanna check this out ... maybe it will help :) ^_^
Click to expand...
(y) thanks a lot bro, Jazak Allah khairn
 
Hassan Ali Abid

Hassan Ali Abid

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for elastic collision momentum b4 = momentum after ......

assume that backward direction ie .ball moving on left hand side is +ve ....then momentum b4 collision is mu2 - (-mu1) and after collision is this : mv2 - mv1

as it is stated that it is elastic so both are equall u2-u1 = v2-v1 ........so ans is 'D'

ps do check its ans from ms .....idk whats its ans but this is the wayhow we solve this :)
 
daredevil

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Reh_456 said:
HI
does anyone know how 2 do this?
9702_s12_qp_12
question 14
thnx in advance!
Click to expand...
keep in mind that the ground is frictionless and when the chair moves down the surface it is resting on will be reacting with forces in the opposite directions to the ones exerted by the ladder
so :
- the ladder when sliding down exerts a downward and 'on the wall force' so the wall exerts an upward force and a force perpendicular to the wall coming out so the resulting force P on the point will be towards top right.
- the weight W will be downwards
- the force exerted by the ground will only be an upward force in reaction to the downward force exerted by the ladder on the ground. no friction force will be acting here as in the start of the question they have mentioned that it is a FRICTIONLESS surface. :)
 
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