Question

1. which of these is the best scientific question for studying the effect on potential energy? what is the length of the ramp? what is the starting height of the cart on the ramp? how fast does a cart roll down a ramp?

Explanation:

Potential energy is related to height. The starting height of the cart on the ramp directly affects its potential energy (using the formula $PE = mgh$, where $h$ is height). The other two questions about ramp - length and cart's speed are not directly about potential energy.

Answer:

What is the starting height of the cart on the ramp?