You time your jump with perfection, and leap just as the sloth slides beneath you. The zombie sloth collides with a loud thump against a wall. You take to opportunity to continue running and sliding your way through the tunnel, following the map. Suddenly you come across a large circular room. There is a locked door with an engraving "What is the mass of my evil pet sloth?" and three buttons with various masses. Not another stupid puzzle from that crazy cabin owner!

You hear the sloth coming up behind you. You and the sloth meet in the center of the circular room and wrestle for a bit. Then you both shove off of each other and go sliding away along the same straight line. You reach the wall of the circular room after 10s and the sloth reaches the wall after 20s. You scramble to the door and do a quick calculation, taking into account that you have a mass of 50kg. Which button do you press?