# Homework Help: Velocity neutron in vacuum

1. Dec 8, 2012

### DRC12

1. The problem statement, all variables and given/known data
What is the de Broglie wavelength of a neutron that has fallen 0.60 in a vacuum chamber, starting from rest?

2. Relevant equations
Not entirely sure
λ=h/mv

3. The attempt at a solution
I can't figure out what the velocity is, I think it would have to do with the change in kinetic energy but I can't figure out what that would be

2. Dec 8, 2012

### Astronuc

Staff Emeritus
Is the distance 0.6 m, cm, mm? Units, as well as magnitude, are rather important to a physics or engineering, or other quantitative problem.

If the neutron is in freefall - what is the acceleration? Knowing the acceleration and distance, one can determine the velocity at that distance.

3. Dec 8, 2012

### DeShark

The other way to look at it, instead of calculating accelerations and integrating back to get velocity, is to look at the Energy. The change in energy is just mg*(change in height) and this goes into the kinetic energy i.e. 1/2 mv^2.

4. Dec 8, 2012

### DRC12

meters

I tried finding the velocity using v2=2ax
and found v to be 3.43m/s
then I plugged that into λ=h/mv
where m=1.67*10-27kg and h=6.67*10-34
and found λ=5.87*10-8

5. Dec 8, 2012

### DRC12

wait for some reason I was using h=3.36E-34 instead of 6.67E-34 I don't even know where that number came from