What work does the force of gravity do on a stone weighing 20 kg when:

What work does the force of gravity do on a stone weighing 20 kg when: a) the stone lies on a rock 100 meters high, b) the stone falls from this rock?

m = 20 kg.
g = 9.8 m / s ^ 2.
hо = 100 m.
h = 0 m.
A -?
Mechanical work A is determined by the formula: A = F * S * cosα, where F is the force that acts on the body, S is the movement of the body under the action of this force, ∠α is the angle between the force F and the displacement S.
The body is affected by gravity: F = m * g, directed vertically downward.
a) when the stone lies on a rock 100 meters high, then the movement of the body is S = 0, and therefore A = 0.
b) when the stone falls from the cliff vertically downwards, then the movement of the talus is S = hо – h and ∠α = 0.
A = m * g * (ho – h) * cos0.
Since cos0 = 1 and h = 0, then A = m * g * ho.
A = 20 kg * 9.8 m / s ^ 2 * 100 m = 19600 J.
Answer: a) A = 0, b) A = 19600 J.