21. A weight trainer lifts a 90.0 kg barbell from a stand 0.90 m high and raises it to a height of 1.75 m. What is the increase in the potential energy of the barbell-Earth system? 21. 22. A child having a mass of 35.0 kg is on a sled having a mass of 5.0 kg. If the child and sled traveling together have a kinetic energy of 260 J from their motion, how fast are they moving