An object mass of \( M_1 \) collides with another object of mass \( M_2 \), which is at rest. After the collision the objects move with equal speeds in opposite direction. The ratio of the masses \( M_2 : M_1 \) is:
\( 3 : 1 \)
\( 1 : 2 \)
\( 1 : 1 \)
\( 2 : 1 \)