A 64.2-kg skateboarder starts out with a speed of 2.21 m/s. He does 98.0 J of work on himself by pushing with his feet against the ground. In addition, friction does -276 J of work on him. In both cases, the forces doing the work are non-conservative. The final speed of the skateboarder is 8.56 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.
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