23) E

No matter which planet you take the object to, the MASS will remain the same as it is on Earth.
Mass of object on Earth = 15N/10 = 1.5 kg

Kinetic energy = Potential energy
Potential energy = mass (1.5kg) x gravitational acceleration (?) x height (10m)

Gravity is 5 times (15N/3N) weaker on the planet. Therefore the acceleration must also be 5 times weaker. Gravitational acceleration = 10/5 = 2 N/kg

Potential energy = 1.5 x 2 x 10 = 30J
Kinetic energy = 30J

The answer is therefore row E.