9)
Using Energy Conservation
Initial Potential Energy = Final Kinetic Energy
m*g*h = K.E

So,
For 5kg
K.E = 5*9.8*80 = 3920 J

For 10kg
K.E = 10*9.8*40 = 3920 J

For 20kg
K.E = 20*9.8*20 = 3920 J

For 25kg
K.E = 25*9.8*16 = 3920 J

This means they all will have same Kinetic Energy when they Reach Grounf, H=0.