Centripetal force + uncertainty

[Wa1337]

Homework Statement

The centripetal force is given by F= (mv²) / r. If the mass is measured to be 2.8 +/- 0.1 kg, the velocity is 14 +/- 2 ms^-1, and the radius 8.0 +/- 0.2 m, find the force on the mass, including the uncertainty.

Homework Equations

F= (mv²) / r

The Attempt at a Solution

0.1/2.8 = .04
2/14 = .14
.2/8.0 = .025

add all up and i got .205

I did the equation and got 69 (2 sig figs) and finally got F = 69 +/- .21

Is that the proper uncertainty answer? If not please help.

 

[AC130Nav]

According to what I read:
http://spiff.rit.edu/classes/phys273/uncert/uncert.html
you have to multiply the value for velocity by two because it's squared.

 

[Wa1337]

edit: nvm

final answer then: F = 270 +/- .21 ? (2 sig figs both)

 

[AC130Nav]

edit: nvm

final answer then: F = 270 +/- .21 ? (2 sig figs both)

I did not say the force was wrong but you changed it; moreover, you still don't have the uncertainty right as I understand it.

I guess I'm not helping.

 

[Wa1337]

I'm sorry I kind of don't get it cause I'm really new to this stuff but my final answer without changing the force is:

F = 69 +/- 14

is that better? thanks

 

[AC130Nav]

I'm sorry I kind of don't get it cause I'm really new to this stuff but my final answer without changing the force is:

F = 69 +/- 14

is that better? thanks

You were closer in your original post.

 

[AC130Nav]

Homework Statement

The Attempt at a Solution

0.1/2.8 = .04
2/14 = .14
.2/8.0 = .025

add all up and i got .205

I did the equation and got 69 (2 sig figs) and finally got F = 69 +/- .21

Is that the proper uncertainty answer? If not please help.

Why is no one helping with this? I'm about to give him the answer as I think it is--it's really not something I do day-to-day but IAW to site I posted previously.

We are surpassing Winston Chruchill adage here "The Americans and the British are a single people divided only by a common language."

 

[NewtonianAlch]

Well he has to get the percentage uncertainties for each of the values.

So for example, for velocity it would 2/14*100 = 14.28% (quite a large uncertainty there)

Since it's squared, the uncertainty would be double: 28.57%

Do this for each of the variables, and add up the percentages. Then your final percentage of the calculated value for force should be your uncertainty in Newtons.