Question

State whether the work done in the following case is positive or negative.

Work done by friction when a person walks on the ground.

Answer 1

The work done is positive. When a person walks, their foot pushes the ground backward, and in response, the ground exerts a frictional force on the foot in the forward direction. Since this frictional force acts in the same direction as the forward displacement of the person, the work done by friction is positive.