Potential energy and a skateboard, only have until 11:30!!!! A 54.5 kg. skateboarder starts out with a speed of 1.95 m/s. He does +80.0 J of work on himself by pushing with his feet against the ground. In addition, friction does -265 J of work on him. In both cases, the forces doing the work are nonconservative. The final speed of the skateboarder is 6.10 m/s Calculate the change (PE = PEf - PE0) in the gravitational potential energy (b) How much has the vertical height of the skater changed? ok so potential energy is PE=MGH buti don't see a vertical height here! Please help!!