How strong is your faith in Principle of Conservation of Energy?

Watch the following interesting video. Do you think the swinging concrete rock, released at the same height as the man's head but on the other side would hit the man when it is allowed to swing towards the man?




The answer lies in energy conservation.
The swinging rock can be likened to a pendulum.
When the rock is swung from its highest point, at that initial release point, all of the energy is gravitational potential energy.
As the rock swings, some of these gravitational potential energy (GPE) is converted to kinetic energy (KE) until the lowest point of its swing when all of the GPE is converted to KE.
As the rock continues in its swing, it ascends (gains in height). Hence, part of its KE is converted to GPE.
At the end of the swing, all of the KE from the lowest point has been converted to GPE.

This amount of GPE is EQUAL to the GPE at the initial release point by energy conservation (assuming energy loss to the surroundings is negligable or non-existent).
Since GPE depends on height, therefore the height the concrete rock can reach CANNOT BE HIGHER than that at the initial release point.

Therefore, the rock will never hit the man if it is released from rest initially at the other end of the swing!

Physics works!