Uncertainties and errors : PHys Unit 3B HELP !

[RedRose91]

hey people.. i need help right now >.<
am having big time with this unit 3B physics...
especially bout all this uncertainties and errors and all..

the big question is HOW THE HELL DO YOU DO IT ??????

am trying and trying to figure it out.. about the percentage uncertainty and estimated uncertainty and all the rules.. plus i practiced a few questions and i got them ALL WRONG !! all of them !!

pleeez pleeeeeeeeez can anyone help me in this .. >.<'
thanks to anyone in advance.. i will really appreciate it..

 

[étudiante]

i use this booklet now.... tho dere is a lot of stuff for A2 only...

 

[RedRose91]

ok to make u guys understand.. here are some of the questions am having trouble with :-

1) In measuring the acceleration of a toy car, the speeds are measured to be (0,20+- 0.02)ms^-1 at time (25+-1)s , and (0.27+-0.02)ms^-1 at time (40+-1)s.
calculate the acceleration of the car, and give the uncertainty in your value.

2) the rate of discharge of a capacitor through a resistor can be used to measure the capacitor's capacitance C using the equation : V = V0e^(1/RC)
At time zero seconds, the voltage across the capacitor (V0) is measured to be (1.5+-0.1)V.
After (20+-1)s it is measured to be (0.8+-0.1)V. The resistor has a value of (4700+-500)ohms.
Using the numerical technique, calculate a value for the capacitance of the capacitor, and the uncertainty in your value.

3) The zero error on a micrometer screw gauge is recorded as +0.04mm. The reading on the gauge when it is placed around a ball bearing is 4.76mm. The micrometer can be read to +-0.005mm.

(a) what's the diameter ? What is its uncertainty ?
(b) what's its radius? its uncertainty ?
(c) calculate volume of the bearing and its uncertainty ?
(d) would it be more precise to measure the volume of the bearings like those above by using a micrometer, or by counting 50 and dropping them into a measuring cylinder of water? Explain.

ANSWERS:-
i do not have the answers for Q3.. but for Q1 & Q2 :-

Q1 : 0.0047ms^-2 ; 70%, or (0.0047+-0.0033)ms^-2 ... (since we are not told whether it is % or absolute uncertainty that is required).

Q2 : +-4.5x10^-3 F , or 2.4 x 10^-3 F .... (depending upon whether you choose greater over smaller, or smaller over greater .. log is not a linear relationship)..


Thanks in advance

 

[RedRose91]

étudiante .. thank you very much ..

 

[étudiante]

étudiante .. thank you very much ..

ur welcum! i hope it helps u...

 

[RedRose91]

Yes.. ^^
i looked at it right now.. and it seems quite helpful indeed
thanks still

 

[RedRose91]

can anyone help me solve those questions i posted above????
thank u