A 57.5 kg skateboarder starts out with a speed of 1.75 m/s. He does +80.0 J of w

Question

A 57.5 kg skateboarder starts out with a speed of 1.75 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 6.15 m/s. (a) Calculate the change (?PE = PEf - PE0) in the gravitational potential energy. J (b) How much has the vertical height of the skater changed? m (c) Is the skater above or below the starting point? above the starting point below the starting point

Explanation / Answer

a) Work done by all forces = change in KE + change in PE

80 - 265 = 0.5*57.5*(6.15^2 - 1.75^2) + delta PE

delta PE = -1184.35 J

b) mgh = delta PE

=> h = 1184.35 / 575 = 2.06 m

c) It is below the starting point as the delta PE is negative => PE decreases

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