# Velocity and kinetic energy of a neutron

1. Aug 20, 2008

### carus88

Calculate the velocity and kinetic energy of a neutron (mass 1.675x10-27kg) that has a wavelength of 0.2nm. How does this compare to the average kinetic energy of a gas molecule at room temperature (0.038eV at 200C)?

1. E=mc^2

2. KE = 1/2 mv^2

I used 1. to calculate the energy which was 1.51 x10^-10 J

Then i subbed the energy into 2. and got a velocity of 4.24 x10^8 m/s

LOL obviously i'm going wrong some where how can a neutron be going faster than light!

CAN SOMEONE HELP PLEASE?

Last edited: Aug 20, 2008
2. Aug 20, 2008

### will.c

First, the expression E=mc^2 does not give the kinetic energy of a particle. Second, even if it did, your method is immune to the given wavelength, so that should give you some idea where you should be looking.

How can you relate the wavelength of a particle to its momentum?

3. Aug 20, 2008

### Dick

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