Left: spear 矛 (developed from the image of a barbed lance [not to be mistaken with 'beforehand': 予]), right: hit/strike 攵 (hand 又 with a stick ノ), strength/force 力
The radical nobun shows a hand or 又 that holds a stick ノ (simplified from the Chinese radical 66 攴 for whip or rap. In this radical, the stick 卜 in the hand 又 is easily cognizable.)
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!