Option 4 is correct as the gravitational force or gravity is the force that pulls all masses towards the centre of the Earth. As long as that object is on Earth, that pull is constant. It is not affected by height and is only affected by mass. So in this case, it doesn’t matter what position or height the marble is at. The amount of gravity acting on the marble will always be constant.

Gravitational potential energy is the amount of energy that an object has by virtue of its position above ground. It is affected by both the mass of the object as well as its relative height above ground. 

@Adwin

Thanks a lot! Been having a problem understanding these type of question but not any more thanks to you! 🙂 

Gravity is different from gravitational force. The experiment is not using different balls, only one ball is used. Frankie.