Two identical spheres move in opposite directions with speeds `v_(1)` and `v_(2)` and pass behind an opaque screen, where they may either cross without touching (Even 1) or make an elastic head-on collision (Event 2).

Options

A. we can never make out which event has occurred
B. we can not make out which event has occurred only if `v_1 =v_2`
C. we can always make out which event has occurred
D. we can always make out which even has occurred only if `v_1=v_2`

Answer

A