Answer
27 m/s
Work Step by Step
In part a we found that the stone takes 1.53 seconds to reach the ground. We also established that the initial velocity, v0 = -12 m/s and that $a = -9.81 m/s^2$
To find the velocity at impact (when it reaches the ground) we use the equation:
v = v0 + at
$v = -12m/s + (-9.81m/s^2)(1.53s) = -27m/s$
The negative here means only the direction, but the speed is the absolute value of the velocity, which is 27 m/s
