# Homework Help: KE of a dust particle?

1. Sep 3, 2007

### user101

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

Find the KE of a dust particle that weighs 1 micrograms traveling at a speed of 1 mm/s

2. Relevant equations

$$E = \frac{mv^2}{2}$$

3. The attempt at a solution

Would this question be applicable to the equation listed above? I thought it was only applicable to electrons in orbit, around a nucleus. I'm questioning this because it's a dust particle...

2. Sep 3, 2007

### cristo

Staff Emeritus
The formula you give holds for any particle moving at speeds not close to the speed of light so, yes, it would be the one to use here.

3. Sep 3, 2007

### Astronuc

Staff Emeritus
The definition of kinetic energy for a given mass m at a speed (magnitude of velocity) v, is given by the equation cited, from electrons to galaxies - but at non-relativistic speeds.

For a collection of particles v would be the mean translational speed, and then there could be rotational kinetic energy.

See - http://hyperphysics.phy-astr.gsu.edu/hbase/ke.html#ke

4. Sep 3, 2007

### user101

Thank you, makes sense now.

Quick question:

If I'm multiplying grams * meters / second... what unit is that? I've been trying to figure that out, can't do it... Ideally I'd like my answer to be in Joules

* I just realized, this should be in the introductory physics section, sorry. I had posted a Q yesterday in this forum for an upper level physics class, so I programmed myself to post this simple Q here.

Last edited: Sep 3, 2007
5. Sep 3, 2007

### Astronuc

Staff Emeritus
Last edited: Sep 3, 2007