posted by Justin .
a 55 kg skateboarder starts out with a speed of 1.8 m/s. he does +80 J of work on himself by pushing with his feet against the ground. in addition, the 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 m/s. Calculate the change in the gravitational potential energy. How much has the vertical height of the skater changed, and is the skater above or below the starting point?
Initial total energy-friction force=final energy.
Let the final energy be KE only, set PE to zero, after all, that point is arbritary.
1/2 m 1.8^2+mgh-frictionwork=1/2 m 6^2
solve for h
1/2 m 1.8^2-265=1/2 m*26
solve for h. If h is negative, then the skater is above the starting point.