Two spheres \( S_1 \) and \( S_2 \) of masses \( m_1 \) and \( m_2 \) collide. Initially \( S_1 \) is at rest and \( S_2 \) moves with velocity \( v \) along x-axis. After collision \( S_2 \) has velocity \( \frac{v}{2} \) in a direction perpendicular to the original direction. The motion of \( S_1 \) after collision is