You will be given a definition of a task first, then some input of the task.
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Electrostatic repulsions normally prevent a positively charged particle from colliding and reacting with a positively charged nucleus, but may be overcome by kinetic energy.
Output:
What normally prevent a positively charged particle from colliding and reacting with a positively charged nucleus, but may be overcome by kinetic energy?