A 52.6-kg skateboarder starts out with a speed of 2.16 m/s. He does 89.2 J of work on himself by pushing with his feet against the ground. In addition, friction does -240 J of work on him. In both cases, the forces doing the work are non-conservative. The final speed of the skateboarder is 5.73 m/s.
(a) Calculate the change (PEf - PE0) in the gravitational potential energy.
(b) How much has the vertical height of the skater changed? Give the absolute value.