I was jealous of her talent, so I tore the canvas she was painting for an art competition to pieces.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means split, but if you split something, you are going to tear it or to rip up it.
In order to get it open, you need to tear and rip up a sack (さく). Sacks don't have tabs or zippers or any of those fancy things. If you want to get at the stuff in a sack you have to tear the top right off!