Given that the collision is elastic and glider 2 is initially at rest (v2,i =0), please use below Eqs. to explain why 1. Glider 2 will be always kicked toward the same direction as glider 1 comes in (v2,f and v1,i have the same sign)
2. Glider 1 will bounce back (v1f and v1,i have opposite sign) if it is lighter than glider 2 (m1= m2).
3. Glider 1 will keep moving forward (v1,f and v1 i have the same sign) if it is heavier than glider 2 (m1 m2)
4. Glider 1 will stop (v1f =0) if it weighs the same as glider 2 (m1= m2)

v1,f= (m1-m2)v1,i + 2m2v2,1/m1+m2
v2,f= (m2-m1)v2,i + 2m1v1,i/m1+m2