2) For the first case,
v2=u2+2as
Here, v=0; a=10 m/s2; s=15 m.
Find u.
u comes out to be 17.32
The objects meet each other after some particular time. Now, for the ball, let distance be S1. Since total distance= 15m, therefore for the stone, the distance after which they will meet is 15-S1 m.
We know, S= ut+ 12at2
Replace with values.
For the ball, S= S1; u=17.32; a=10.
For the stone, S=15-S1; u=0; a=10.
So the equations are:
     S1= 17.32t -5t2
15-S1=             5t2
Add the equations.
t comes out to be 0.87
Therefore S1=10.75
So, 15-S1 is= 4.25
So, their ratio= 10.754.25= 2.53...