Calculation of the velocity uncertainty

[dba]

Homework Statement

I need to calculate the uncertainty for the velocity v_1=(cart length)/t_1. The cart length is constant.

Homework Equations

That is what I am not sure about. I need to use the rule "dividing by a constant" to find the uncertainty. Is that

result q=B/x ,where B is the constant and

∆q=|1/B|* ∆x

The Attempt at a Solution

The problems is I get the units wrong when I apply this. i need m/s
My ∆t=0.0001s and the cartmass=0.129kg

∆v_1= |1/0.129m|* 0.0001s

This would give me s/m?

So I guess my fomrmula is wrong. Can someone help me finding the right approach to calculate the uncertainty?
Thanks.

 

[gneill]

Basic Propagation of Errors of Precision

For z = x + y or z = x - y, then

$$\Delta z = \sqrt{\Delta x^2 + \Delta y^2}$$

For z = x*y or z = x/y then

$$\Delta z = z \sqrt{\left(\frac{\Delta x}{x}\right)^2 + \left(\frac{\Delta y}{y}\right)^2}$$

For z = xⁿ,

$$\Delta z = n x^{n-1} \Delta x$$