While a skateboarder coasts to a stop on level ground
PHYSICS · Single correct · CBSE · Physics · Work and Energy · Work and Energy
Problem
While a skateboarder coasts to a stop on level ground, a student chooses the skateboarder alone as the system and writes that the system’s mechanical energy is conserved. Which of the following best explains why the student’s conclusion is incorrect?
(a) Gravitational potential energy is zero on level ground, so without it energy conservation cannot be applied.
(b) Because the static friction between the skateboarder’s feet and the board does no work, no external work acts on the skateboarder and its mechanical energy is conserved.
(c) Kinetic friction acting on the wheels does external work on the skateboarder, removing mechanical energy from the system.
(d) Energy that becomes thermal energy is still mechanical energy, so the skateboarder’s mechanical energy does not change.