Kinetic energy = (1/2) (mass) (speed)²
In order to make the rock move at 25 m/s, you must give it
(1/2) (7 kg) (25 m/s)² =
(3.5 kg) (625 m²/s²) =
2,187.5 joules of kinetic energy.
That energy has to come from somewhere.
If you're trying to give the rock that speed by throwing it,
then the energy has to come from your throwing muscles.
