How the hell would throwing a rock at a cliff make it crack and fall off like that?
It would be near impossible to propell it that fast with your bare hands, since it would probably require the force of a battering ram, which would have more than one person and the machine itself(the ram) would multiply the force, so you would need the strength of maybe, 12 men to do the job.
Now if you had some dynamite...
Jumping off the spike with your hand would be near impossible, for one you couldnt get a good enough grip and for two you couldnt generate enough force to move your entire body.