Question

At what point on a roller coaster is the gravitational potential energy (GPE) the lowest?

Answer 1

At a time when the roller coaster is located nearest to the ground.

Explanation:

Gravitational potential energy of an object is equal to the product of three things
1. mass `m` of the object
2. Acceleration due to gravity `g`, which is `=9.81 ms^-2`
3. Height `h` above the surface of earth where the object is positioned.

It is given by the expression

`PE=mgh`

Now mass and acceleration due to gravity do not change, and in a roller coaster only variable is its height above the ground.

From the above expression it follows that potential energy is lowest when `h` is minimum.