Answer:
y = 6.92[m]
Vf = 16.305[m/s]
Step-by-step explanation:
To solve this problem we must use the following kinematics equations, where we must first find the final velocity.

where:
Vi = initial velocity = 11.4[m/s]
Vf = final velocity [m/s]
t = time = 0.5[s]
g = gravity acceleration = 9.81[m/s^2}
Note: the positive sign in the equation above is because the acceleration of gravity goes in the direction of the motion of the rock.
Vf = 11.4 + (9.81*0.5)
Vf = 16.305 [m/s]
Now we can calculate how far the rock goes, using the following equation:
![v_(f) ^(2)= v_(i) ^(2)+(2*g*y)\\v_(f) ^(2)- v_(i)^(2) = 2*g*y\\y = (v_(f) ^(2)- v_(i)^(2))/(2*g) \\y = (16.305^(2)-11.4^(2) )/(2*9.81)\\ y=6.92[m]](https://img.qammunity.org/2021/formulas/physics/college/o1vbekp5ln39i6ubgplhuttiulrburkx5f.png)
Therefore the Rock will be (70 - 6.92) = 63.07 [m] above the water level