Calculate Speed of Recoiling Hydrogen Atom After Transition to Ground State

[the armed pacifist]

A hydrogen atom, initially at rest in the n = 4 quantum state, undergoes a transition to the ground state, emitting a photon in the process. What is the speed (in terms of m/s) of the recoiling hydrogen atom?

anyone knows what to do? i calculated the energy difference and got 12.75 eV and i calculated the potential energy as well, but i don't know which mass to assign the atom...

any help is appreciated...

 

[Doc Al]

(1) What's conserved during the emission?
(2) You can look up the mass of a hydrogen atom!

 

[the armed pacifist]

reply

well, that's the thing- the problem doesn't state anything more than I put on there... the mass of a hydrogen atom will be that of 1 proton, but I'm not sure if that's what i should look for...

any thoughts?

 

[Doc Al]

You don't need any more information to solve the problem. What's the answer to my first question? (Hint: In any kind of "explosion", what's conserved?)