If potential energy and kinetic energy are equal then,
PE = mgh = KE = (1/2)mv^2
Where,
m = mass of the object,
g = acceleration due to gravity (9.81 m/s^2),
h = height of the object,
v = velocity of the object.
Given,
mass= 89kg,
height= 4 meters,
Now,
mgh = (1/2)mv^2
89 kg * 9.81 m/s^2 * 4 m = (1/2) * 89 kg * v^2
v^2 = 2 * 9.81 m/s^2 * 4 m
v^2 = 78.48 m^2/s^2
v = sqrt(78.48 m^2/s^2) = 8.86 m/s
Therefore, the velocity of the object is 8.86 m/s.