capable:

adj. 有能力的有才干的容许……的可以做（某事）的综合性的有资格的

I think he is capable of accomplishing the challenge.

我认为他是有能力完成这个挑战的。

competent:

adj. 胜任的有能力的能干的足够的

The leaders sent him to Africa because they thought he was competent for the job.

领导们派他去非洲，因为他们认为他能胜任这项工作。