# Easy uncertainty question, I need HELP

1. Feb 12, 2012

### Alipepsi

1. The problem statement, all variables and given/known data
Hey there, I need some help with uncertainties and how to find the speed of a moving object. I have tried to solve the problem several times but my answer seems to be wrong.

Formula for speed : v=d/t
My uncertainties: 0.5cm (distance) and 0.5s for time. The uncertainties were measured with the same analog.
I did the experiment 15 times and got different speed result of the object each time. The total sum of the speeds ( 15 trials) was 44.99s. The average of that is 2.99 (15/44.99)
Oh and my measuring device was 228cm long (exact)

I need to find out the speed and the uncertainties

2. Relevant equations

Formula to use : v=d/t
3. The attempt at a solution

v=d/t
= (228 +\- 0.5)m/(2.99+\- 0.5)s
228 divided by 0.5 = 456%
2.99 divided by 0.5= 5.78%
456% +5.78%=461.98%

so now 461.98% * 76.2 ( which I got by diving 288 and 2.99)
my final answer was v=76.25m? +\- 39%..
I'am confused..

2. Feb 12, 2012

### Alipepsi

Actually spend hours on trying to solve this :S
Help will be greatly appreciated!

3. Feb 12, 2012

### Alipepsi

anyone?

4. Feb 12, 2012

### ojs

Check out this site here: http://www.rit.edu/cos/uphysics/uncertainties/Uncertaintiespart2.html [Broken]

Last edited by a moderator: May 5, 2017
5. Mar 11, 2012

Okey, thanks