Work By Friction On Straight Path — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Work Done by Friction on a Straight Path This formula applies when an object moves along a straight path against kinetic friction, where the normal force (N) and the coefficient of kinetic friction ( k) are constant. Work done is defined as the dot product of force and displacement: W = F d . The kinetic friction force ( f k) always opposes the displacement ( d ). The magnitude of the friction force is f k = k N . Since the angle between f k and d is 180 , W fr = f k d (180 ) = -f k d . Substituting the friction magnitude yields W fr = - k N d . k 0 N 0 d 0 Forgetting the negative sign, which indicates that the work done by friction always removes energy from the system. Confusing the coefficient of kinetic friction ( k) with the coefficient of static friction ( s). Assuming the normal force (N) is always equal to the gravitational force (mg), ignoring vertical accelerations or applied forces.