# velocity and kinetic energy of a neutron

by carus88
Tags: quantum physics, x-ray tube
 P: 14 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?
 P: 374 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?
 HW Helper Sci Advisor Thanks P: 24,422 This is the same as http://www.physicsforums.com/showthread.php?t=251160 carus88, don't multiple post.

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