Strength

The Japanese word 力 specifically means physical strength or physical power.

The Japanese word 強力 also means "strong; powerful" and is composed of the kanji 強 (read kyou) meaning "strong; powerful" and 力 (read ryoku) meaning "strong; powerful". 強力 can mean either physical or mental strength and can be used in the sense of "you need to be strong to make it in this world".