I.E.IRODOV PROBLEMS IN GENERAL PHYSICS 1.121

A body of mass m is slowly hauled up the hill by force F which at each point was directer along a tangent to the trajectory. Find the work performed by this force, if the height of hill is h, the length of its base is l , and the coefficient of friction is k. STEPS AND CONCEPT This video provides a detailed, step-by-step physics solution to I.E. Irodov Problem 1.121 (0:40). The problem involves calculating the work performed by an external force required to slowly haul a body of mass up a hill of height and base length given a coefficient of friction (0:50 - 2:55). Key concepts covered in the solution: Slow Motion Principle: The speaker explains that "slowly hauling" the body implies there is no change in kinetic energy, meaning the acceleration is zero and the net force is balanced (5:36 - 6:40). Work-Energy Theorem: To find the external work, the narrator utilizes the work-energy theorem, which states that the sum of work done by conservative forces (gravity), non-conservative forces (friction), and the external force equals the change in kinetic energy (6:55 - 7:20). Work Done by Friction: Because friction is a non-conservative force depending on the path, the narrator performs an integration over the trajectory, using the relation to simplify the expression, ultimately finding the work done by friction to be (8:13 - 11:47). Final Calculation: By summing the work contributions—where the work done by gravity is and friction is —the final result for the external force's work is determined to be (12:08 - 12:42).