At highest point, velocity = 0, height (potential energy) is max
at lowest point, velocity(Kinetic energy) is max, height (PE) is reduced
total energy at 2 points is equal --- conservation of energy. in the other words, potential energy transform to kinetic energy when decending.
PE reduce = KE increase
PE@highest - PE@lowest = KE@lowest - KE@highest
mg(180) - mg(60) = 0.5mv^2 - 0
g(180-60) = 0.5v^2
work from here
... remark ... unit of v is cm/s