# EMERGENCY HELP NEEDED PLZZ

Discussion in 'International A And AS Level' started by MysteRyGiRl, May 30, 2011.

1. ### MysteRyGiRl

Messages:
3,063
1,832
Trophy Points:
173
Gender:
Female
Location:
h0me sWeet h0me
heyy can sm1 plz help me out wd AS physx uncertainity question? given below
The density of the material of a rectangular block is determined by measuring the mass and
linear dimensions of the block. The table shows the results obtained, together with their
uncertainties.
mass = (25.0 ± 0.1) g
length = (5.00 ± 0.01) cm
breadth = (2.00 ± 0.01) cm
height = (1.00 ± 0.01) cm
The density is calculated to be 2.50 g cm–3.
What is the uncertainty in this result?
i hv board papers nxt ...2 nxt week n i wd rely appreciate sm1s help thank u

3. ### MysteRyGiRl

Messages:
3,063
1,832
Trophy Points:
173
Gender:
Female
Location:
h0me sWeet h0me
ummmm 1 more question plzz
A quantity x is to be determined from the equation
x = P – Q.
P is measured as 1.27 ± 0.02 m.
Q is measured as 0.83 ± 0.01 m.
What is the percentage uncertainty in x to one significant figure?

4. ### Apoclaypse

Messages:
10
0
Trophy Points:
3
Gender:
Male
Location:
when solving these u have to rember one thing ,, uncertainnities are always added.! right mate!

ok on question now,, density =mass/volume,, so find v first and error in we.
V= length x width x height. 2*5*1= 10
V=10 uncertainity would be

x/10=.01/2 + .01/5 +.01/1 by solving this we get x=.17 now put this into d=m/v

x/2.5=.1/25+.17/10 uncertainty in density is .05

5. ### MysteRyGiRl

Messages:
3,063
1,832
Trophy Points:
173
Gender:
Female
Location:
h0me sWeet h0me
thank u soooooooo much
cd u plz answer da scnd 1 too?

6. ### Apoclaypse

Messages:
10
0
Trophy Points:
3
Gender:
Male
Location:
Subtract p from q and add their uncertainity!! 1.27-.83=.44 .01+.02=.03
x=.44±.03

7. ### Apoclaypse

Messages:
10
0
Trophy Points:
3
Gender:
Male
Location:
there u go!

8. ### thunderingthunder

Messages:
339
106
Trophy Points:
53
Gender:
Female
Location:
Multan,Pakistan
ATC:x=P-Q..
So....x=1.27-0.83=0.44....
%age uncertainty is (error in x/x)x100....we dont have error in x..we will calculate it...lyk this:
error in x/x=error in P/P+error in Q/Q
error in x=0.01..
therefore %age uncertainty in x=(0.01/0.44)x100=2.2%..
therefore %age uncertainty in x=2.2%..
hope this helps

9. ### MysteRyGiRl

Messages:
3,063
1,832
Trophy Points:
173
Gender:
Female
Location:
h0me sWeet h0me
ummm da answer 4 da second question is supposed 2 b 7% :shock:
hw do v get dat???
btw thnx 4 helping out

10. ### Xenon

Messages:
350
62
Trophy Points:
38
maybe thundering thunder made a typing mistake, the error in x will be 0.03 (0.02 + 0.01 )instead on 0.01. this will give u a value of 6.8%.

11. ### MysteRyGiRl

Messages:
3,063
1,832
Trophy Points:
173
Gender:
Female
Location:
h0me sWeet h0me
ohhhkk
thanx guyzz

Messages:
339