PHYSICS · Single correct · CBSE · Physics · Work and Energy · Work and Energy
Problem
A toy car is pushed along a rough track, released, and eventually rolls back to its starting point at a slower speed before stopping. Considering only the car–track system, which statement most accurately characterizes the net work done by friction and the associated change in the system’s mechanical energy for this round trip?
(a) Friction does no work because static friction is present whenever the car is momentarily at rest.
(b) The net work done by friction is negative, and the mechanical energy lost equals the magnitude of that work.
(c) The net work done by friction is zero because the car returns to its original position.
(d) Friction does positive work on the outbound trip and negative work on the inbound trip, so the two contributions exactly cancel.