Posted by Justin on Saturday, December 4, 2010 at 9:27pm.
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?

Physics  bobpursley, Saturday, December 4, 2010 at 9:47pm
Initial total energyfriction 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+mghfrictionwork=1/2 m 6^2
solve for h
1/2 m 1.8^2265=1/2 m*26
solve for h. If h is negative, then the skater is above the starting point.
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