Question

An electron, mass m = 9.11 × 10-31 kg, collides head-on with a neutral atom, mass M = 118.57 × 10-27 kg, initially at rest. As a result of the collision, a characteristic amount of energy E = 85 × 10-17 J is stored internally in the atom. What is the minimum initial speed that the electron must have?


I didn't understand what 'energy is stored' means.
I thought < 1/2*m*v^2 + 1/2*M*0^2 = E > would make sense, but again not sure about the energy part.

Answer 1

well, it is not clear but I think I would assume that the electron stuck with the atom
therefore assume first that momentum is conserved
m v = (m + M) V
solve for V, the final speed of the combined particle
Now what does "stored" mean?
I suspect that "stored" does not include the kinetic energy of the combined particle
so
stored might be (1/2) m v^2 - (1/2) (m+M) V^2