# Homework Help: Units - is this m/s or mm/s?

1. Jan 21, 2009

### dcramps

Units -- is this m/s or mm/s?

1. The problem statement, all variables and given/known data
N/A

2. Relevant equations
Continuity
A1*v1=A2*v2

A=pi*r²

3. The attempt at a solution

I've solved a problem as follows

(pi * 10.0mm²)(0.200m/s)=(pi * 2.50mm²)(v2)
3.20 xx/s = v2

I am pretty sure it's in m/s, but having the radii in millimeters is confusing me. I would convert all to meters, but I am required to solve using 3sf, so I would lose accuracy on the 2.50mm.

Am I correct in thinking the answer is in m/s?

2. Jan 21, 2009

### phreak

Re: Units -- is this m/s or mm/s?

You can never lose accuracy by converting millimeters to meters, and vice-versa, since the two are separated by a constant. You have the right idea - turn everything into meters, and if you want, you can turn the end product back into millimeters.

3. Jan 21, 2009

### dcramps

Re: Units -- is this m/s or mm/s?

Heh, I converted 2.50mm to 0.025m and, for whatever reason, I got the idea in my head that I would have to reduce it to 0.020m to still have 3sf. I went back and did a bit of review on sf and figured it out :p

Thanks for the response!

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