i dont understand those.. Help An atom of mass M is initially at rest, in its gr

Question

i dont understand those.. Help

An atom of mass M is initially at rest, in its ground state. A moving (nonrelativistic) electron of mass mecollides with the atom. The atom+electron system can exist in an excited state in which the electron is absorbed into the atom. The excited state has an extra, "internal," energy E relative to the atom's ground state.(Figure 1)

Find the kinetic energy Ke that the electron must have in order to excite the atom. Express your answer in terms of E, mc, and M. What is the least possible initial kinetic energy Kmin the oxygen atom could have and still excite the cesium atom? Express your answer in electron volts, to one decimal place.

Explanation / Answer

Answer question

conservation of momentum

me v = (me + M) vfinal
vfinal = me v/(me + M)

conservation of energy
1/2 me v^2 = 1/2 (M + me) vfinal^2 + E

1/2 me v^2 = 1/2 (M + me) me^2 v^2/(M + me)^2 + E

1/2 me v^2 = 1/2 me^2 v^2/(M + me) + E

but K = 1/2 me v^2

K = me/(M + me) K + E

(1 - me/M + me) K = E

M/(M + me) K = E

K = (M + me) E/M

c) need part b to do this part

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