Question

A 61.5-kg skateboarder starts out with a speed of 1.71 m/s. He does 105 J of work on himself by pushing with his feet against the ground. In addition, friction does -298 J of work on him. In both cases, the forces doing the work are non-conservative. The final speed of the skateboarder is 5.93 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.

Answer 1

---------------------------- solution of part a --------------------------------------

Mass of the skateboarder = 61.5 kg

Initial speed = 1.71 m/s

work done by person = 105 J

work done by friction = -298 J

final speed = 5.93 m/s

Using the concept of total energy conservation we can write

So the change in gravitational potential energy is 1184.4 J

------------------------------ solution of part b -----------------------------

the change in potential energy can be use to calculate the change in vertical height using

So the change in height of the skater is 1.96 m