A 54.5 kg. skateboarder starts out with a speed of 1.90 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 5.90 m/s.

Question

A 54.5 kg. skateboarder starts out with a speed of 1.90 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 5.90 m/s.
(a) Calculate the change (ΔPE = PEf - PE0) in the gravitational potential energy.

Damon · Answer

initial Ke = (1/2)(54.5)(1.9)^2 = 98.4 J final Ke = (1/2)(54.5)(5.9)^2 = 948.6 J increase in Ke = 85.2 J PEf + Ke f = PEi + 80 - 265 + Ke i PEf - PEi = 80 - 265 + 98.4 - 948.6 = - 1035 J