Question

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 (event 1) or make an elastic head-on collision (event 2) -

• 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 make out which event has occurred only if $v_{1}=v_{2}$

Answer 1

Answer: (A)

Balls are identical and velocity exchanges if elastic head on collision occurs.