UPSC 2015 CDS I GK Paper

Statement (a) is correct. An object is raised to a height of 3 m from the ground. It is then allowed to fall on to a table 1 m high from the ground level.
Total energy at 3 m = potential energy at 3 m + kinetic energy at 3 m
Potential energy at 3 m = mass × g × 3
Kinetic energy at 3 m = 0
Total energy at 3 m = 3 mg + 0= 3 mg
Total energy at 1 m = potential energy at 1 m + kinetic energy at 1 m
Potential energy at 1 m = mass × g × 1
Kinetic energy at 1 m = 0
Total energy at 1 m = 1 mg + 0= 1 mg
Hence, potential energy at 1 m decreases by two-thirds its original value of total energy.