Answer: 15,000 units, because total energy is 50,000 units
Explanation:
According to law of conservation of energy, energy remains conserved. It only transforms from one form to another.
The total energy here is the sum of kinetic and potential energy.
At 100 meters, total energy = Kinetic energy + potential energy = 0 units + 50000 units = 50000 units
At 30 meters, total energy = Kinetic energy + potential energy = 35000 units + x units = 50000 units
x units = 15000 units
Thus if the kinetic energy has increased from 0 to 35000 units, the potential energy must decrease from 50000 to 35000 units to keep the energy conserved.