A nucleus moving with a velocity `vecv` emits an `alpha` -particle. Let the velocities of the `alpha` -particle and the remaining nucleus be `vecv_(1)` and `vecv_(2)` and their masses be `m_(1)` and `m_(2)`.

Options

A. `vecv, vecv_(1)` and `vecv_(2)` must be parallel to each other.
B. None of the two of `vecv, vecv_(1)` and `vecv_(2)` should be parallel to each other
C. `vecv_(1) + vecv_(2)` must be parallel to `vecv`
D. `m_(1)vecv_(1) + m_(2) vecv_(2)` must be parallel to `vecv`

Answer

D