9) 7.2 m

Kinetic energy = 0.5mv²
Potential energy = mgh

Since Kinetic energy = Potential energy,

0.5mv² = mgh
0.5 x 144 = 10 x h
h = 72 ÷ 10 = 7.2 m

OR

We can just use a SUVAT equation

v² – u² = 2as

144 – 0 = 2 x 10 x s
s = 144 ÷ (2 x 10) = 7.2 m